E.164 numbering and dial string normalization

See also

Sources

1. 1
   Amazon Connect StartOutboundVoiceContact requires DestinationPhoneNumber and SourcePhoneNumber in E.164, validated against the pattern \+[1-9]\d{1,14}$.

   StartOutboundVoiceContact - Amazon Connect API Reference · Request Body: DestinationPhoneNumber; SourcePhoneNumber · Checked 2026-09-23
2. 2
   Amazon Connect does not allow outbound calls to UK numbers with the 447 prefix by default; a service quota increase is needed first.

   StartOutboundVoiceContact - Amazon Connect API Reference · Opening notes · Checked 2026-09-23
3. 3
   In CUCM calling party normalization, globalization converts a local calling number to international form by adding country and area codes, and localization strips those prefixes for regional display so a phone can return the call without editing the number.

   System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Calling Party Normalization · Calling Party Normalization Overview · Checked 2026-09-23
4. 4
   CUCM 15 supports sending the '+' international escape character on outgoing calls over SIP trunks and MGCP gateways; H.323 gateways do not support it and QSIG trunks do not attempt to send it.

   System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Calling Party Normalization · International escape character (+) section · Checked 2026-09-23
5. 5
   Because SIP has no number type, CUCM SIP trunks apply only the Incoming Number prefix settings configured for calling party number type Unknown.

   System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Calling Party Normalization · Restrictions section · Checked 2026-09-23
6. 6
   ITU-T E.123 (02/2001), the Recommendation on notation for national and international telephone numbers, is in force together with Erratum 1 (05/2008), Erratum 2 (06/2022) and Amendment 1 (05/2008).

   E.123 : Notation for national and international telephone numbers, e-mail addresses and web addresses · Version rows marked In force · Checked 2026-09-23
7. 7
   E.164 (02/2026) is edition 7 of the Recommendation and replaces edition 6, E.164 (11/2010).

   ITU-T Recommendation database: E.164 The international public telecommunication numbering plan · History table, editions 6 and 7 · Checked 2026-09-23
8. 8
   The E.164 (02/2026) summary defines eight categories of international numbers: Geographic Areas, Global Services, Other Global Services, Global Satellite Services, Networks, Groups of Countries, Trial resources, and IoT/M2M services and applications.

   ITU-T Recommendation database: E.164 The international public telecommunication numbering plan · Summary paragraph (02/2026 edition) · Checked 2026-09-23
9. 9
   In ENUM the Application Unique String is the fully qualified E.164 number with all non-digit characters removed except the leading '+'.

   RFC 6116: The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM) · Section 3.1 · Checked 2026-09-23
10. 10
    To convert an E.164 number into an ENUM domain name, remove all non-digits, reverse the digits, put a dot between each digit and append e164.arpa.

    RFC 6116: The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM) · Section 3.2 (example +44-20-7946-0148 to 8.4.1.0.6.4.9.7.0.2.4.4.e164.arpa.) · Checked 2026-09-23
11. 11
    RFC 6116 (ENUM) is a Standards Track document published in March 2011 that obsoletes RFC 3761.

    RFC 6116: The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM) · Document header · Checked 2026-09-23
12. 12
    libphonenumber documents that Germany has assigned working numbers longer than the ITU 15-digit maximum.disputed

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 16: All valid phone numbers follow the ITU specifications · Checked 2026-09-23
13. 13
    The in-force edition of ITU-T Recommendation E.164 is E.164 (02/2026), approved on 2026-02-13.

    ITU-T Recommendation database: E.164 The international public telecommunication numbering plan · History table, edition 7 row; approval date field · Checked 2026-09-23
14. 14
    E.164 (02/2026) treats IoT/machine-to-machine services and applications as a separate number category and cites definition clause 3.2.17 for it.

    ITU-T Recommendation database: E.164 The international public telecommunication numbering plan · Summary paragraph, IoT/M2M reference to clause 3.2.17 · Checked 2026-09-23
15. 15
    libphonenumber documents that in Italy the leading zero of a domestically formatted number is part of the number and is kept in international format (for example +39 0…), so stripping a trunk zero is not a universal normalization rule.

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 21: A leading zero in numbers formatted for domestic usage can always be discarded · Checked 2026-09-23
16. 16
    libphonenumber provides only the carrier originally assigned a number range, not the current carrier of a ported number.

    google/libphonenumber README · README, carrier mapping FAQ note · Checked 2026-09-23
17. 17
    libphonenumber formats numbers as E164 (+41446681800), INTERNATIONAL (+41 44 668 18 00) or NATIONAL (044 668 18 00), and can also format them as RFC 3966.

    google/libphonenumber README · README, Quick Examples / formatting · Checked 2026-09-23
18. 18
    In libphonenumber, isPossibleNumber checks only length information, while isValidNumber does full validation using both length and prefix metadata.

    google/libphonenumber README · README, Highlights of functionality · Checked 2026-09-23
19. 19
    ITU-T E.164 limits an international telephone number to at most 15 digits, counting the country code but not the international prefix.

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 16: All valid phone numbers follow the ITU specifications · Checked 2026-09-23
20. 20
    libphonenumber warns against storing phone numbers as numeric types because leading zeros can be significant and part of the number.

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 25: Phone numbers are numbers · Checked 2026-09-23
21. 21
    libphonenumber documents that the '+' is part of the E.164 format for international numbers and is not optional.

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 23: The plus sign in front of phone numbers in international format is optional · Checked 2026-09-23
22. 22
    ITU lists the E.164 editions 11/88, 08/91, 05/97, 02/05 and 11/10 as superseded.

    E.164 : The international public telecommunication numbering plan (version listing) · Version rows marked Superseded · Checked 2026-09-23
23. 23
    Teams normalization rules whose first token is optional (for example ^0?(999)$) are not supported on 3PIP devices and must be split into two rules.

    Normalization rules for Microsoft Teams dial plans · Creating normalization rules, Note on 3pip devices · Checked 2026-09-23
24. 24
    The Teams client applies the user's effective dial plan to every outbound call, including calls placed from call history and from telephone-number links.

    Microsoft Teams Dial plans for phone call routing · Dial plans and routing considerations · Checked 2026-09-23
25. 25
    A Teams dial plan is a named set of normalization rules that translate user-dialed strings into a standardized format, typically E.164, for authorization matching and routing.

    Microsoft Teams Dial plans for phone call routing · What are dial plans? · Checked 2026-09-23
26. 26
    Teams has three dial plan scopes: a Microsoft-managed, non-configurable service dial plan for each country or region, a tenant (Global) dial plan, and user dial plans.

    Microsoft Teams Dial plans for phone call routing · Dial plan scopes and a user's effective dial plan, first table · Checked 2026-09-23
27. 27
    Teams normalization rules are written as .NET Framework regular expressions, each with a match pattern and a translation, that turn dial strings into E.164.

    Normalization rules for Microsoft Teams dial plans · Creating normalization rules · Checked 2026-09-23
28. 28
    To avoid double normalization, Microsoft recommends that Direct Routing customers normalize to a '+' form in dial plans and then remove the '+' with a route-based translation rule if the SBC needs it.

    Translate phone numbers for Direct Routing · Route-based number translations - for outbound calls, Note · Checked 2026-09-23
29. 29
    When Teams processes a dialed number, user dial plan normalization rules take precedence over the tenant Global dial plan, and the tenant dial plan takes precedence over the service country dial plan it is merged with.

    Microsoft Teams Dial plans for phone call routing · Dial plan scopes and a user's effective dial plan, precedence paragraph and effective dial plan table · Checked 2026-09-23
30. 30
    Example 4 in Microsoft's Direct Routing translation article appears internally inconsistent: it describes an outbound call but names Inbound* parameters, and its translated To header shows 4255555555 rather than the 4255550100 in the Request-URI.inferred

    Translate phone numbers for Direct Routing · Example 4: Outbound call using a four-digit non-E.164 number (table); also To header in Example 3 · Checked 2026-09-23
31. 31
    A Teams number can carry an extension of 1 to 12 digits after a case-insensitive ';ext=' delimiter; if an extension is assigned, the inbound dialed number must include it for RNL to match.

    Microsoft Teams Dial plans for phone call routing · Number lookup for inbound calls, Extension bullet and following example · Checked 2026-09-23
32. 32
    Teams matches normalization rules from top to bottom, applies the first rule that matches and does not evaluate any later rules.

    Normalization rules for Microsoft Teams dial plans · Opening section, paragraph on rule order · Checked 2026-09-23
33. 33
    Microsoft enforces a maximum of 50 normalization rules in a single Teams dial plan.

    Normalization rules for Microsoft Teams dial plans · Note following the opening section · Checked 2026-09-23
34. 34
    A Teams tenant can have at most 1,000 tenant dial plans.

    Microsoft Teams Dial plans for phone call routing · Dial plans and routing considerations · Checked 2026-09-23
35. 35
    For Teams Reverse Number Lookup, a Calling Plan or Operator Connect number is stored in E.164 format, whereas a Direct Routing number is stored as 3 to 38 digits without common symbols.

    Microsoft Teams Dial plans for phone call routing · Number lookup for inbound calls · Checked 2026-09-23
36. 36
    If a user's effective Teams dial plan applies no normalization rule to a dialed number, the Teams service dial plan prepends '+CC', where CC is the country or region code of the user's usage location.

    Translate phone numbers for Direct Routing · Route-based number translations - for outbound calls, Note · Checked 2026-09-23
37. 37
    Direct Routing allows at most 400 number translation rules in total, with pattern strings up to 1024 symbols and translation strings up to 256 symbols.

    Translate phone numbers for Direct Routing · Considerations, Note · Checked 2026-09-23
38. 38
    Direct Routing translation rules are attached to an SBC through four gateway parameters: InboundTeamsNumberTranslationRules, InboundPSTNNumberTranslationRules, OutboundTeamsNumberTranslationRules and OutboundPSTNNumberTranslationRules, and they are applied in the order they are listed.

    Translate phone numbers for Direct Routing · Considerations; Configuring translation rules with PowerShell · Checked 2026-09-23
39. 39
    The phone-context value of a local tel URI is a domain name or a global number prefix, and it is not a prefix that can be prepended to turn the local number into an E.164 number.

    RFC 3966: The tel URI for Telephone Numbers · Section 5.1.5 Local Numbers · Checked 2026-09-23
40. 40
    The tel URI defines an 'extension' parameter for extensions and an 'isdn-subaddress' parameter for ISDN subaddresses.

    RFC 3966: The tel URI for Telephone Numbers · Sections 5.2 ISDN Subaddresses and 5.3 Phone Extensions · Checked 2026-09-23
41. 41
    RFC 3966 requires a tel URI global number to consist of the country code and the national significant number, as specified in E.123 and E.164.

    RFC 3966: The tel URI for Telephone Numbers · Section 5.1.4 Global Numbers · Checked 2026-09-23
42. 42
    Under RFC 3966, two tel URIs can be equivalent only if both are global numbers or both are local numbers, so a global number never equals a local number.

    RFC 3966: The tel URI for Telephone Numbers · Section 4 URI Comparisons · Checked 2026-09-23
43. 43
    In a tel URI, a global number is identified by a leading '+' character.

    RFC 3966: The tel URI for Telephone Numbers · Section 5.1.4 Global Numbers · Checked 2026-09-23
44. 44
    A tel URI local number must carry a phone-context parameter that identifies the scope in which it is valid.

    RFC 3966: The tel URI for Telephone Numbers · Section 5.1.5 Local Numbers · Checked 2026-09-23
45. 45
    RFC 3966, which defines the tel URI, is a Standards Track document published in December 2004 that obsoletes RFC 2806.

    RFC 3966: The tel URI for Telephone Numbers · Document header · Checked 2026-09-23
46. 46
    Visual separators in a tel URI, such as hyphens, dots and parentheses, are for readability only and are not used for URI comparison or for placing the call.

    RFC 3966: The tel URI for Telephone Numbers · Section 5.1.1 Separators · Checked 2026-09-23
47. 47
    E.164 (02/2026) includes resources for trials as a number category and cites definition clause 3.2.22 for it.

    ITU-T Recommendation database: E.164 The international public telecommunication numbering plan · Summary paragraph, Trial reference to clause 3.2.22 · Checked 2026-09-23
48. 48
    libphonenumber warns that a number that is valid and connects today may be disconnected later, so validity checks are only true at a point in time.

    Falsehoods Programmers Believe About Phone Numbers · Falsehood 6: Phone numbers that are valid today will always be valid · Checked 2026-09-23
49. 49
    A Webex Calling dial plan can hold up to 10,000 dial patterns, and the CSV upload also accepts up to 10,000.

    Configure trunks, route groups, and dial plans for Webex Calling · Dial plan section, limits · Checked 2026-09-23
50. 50
    Webex Calling Control Hub allows up to 1,000 numbers per add operation and activation of 500 numbers at a time.

    Manage phone numbers in Control Hub · Add and activate phone numbers sections · Checked 2026-09-23
51. 51
    Webex Calling premises dial plans accept E.164 patterns, which begin with '+', enterprise patterns for on-premises extensions or ESN numbers, and SIP URI domain patterns.

    Configure trunks, route groups, and dial plans for Webex Calling · Dial plan section, dial pattern formats · Checked 2026-09-23
52. 52
    Webex Calling ignores the outbound dial digit requirement for outbound calls dialed in E.164 format, and Cisco highly recommends E.164 for incoming and outgoing PSTN calls.

    Configure your Webex Calling dial plan · External dialing settings · Checked 2026-09-23
53. 53
    Webex Calling internal extensions can be 2 to 10 digits long (default 4), and location routing prefixes 1 to 7 digits, with the first digit being the org's steering digit.

    Configure your Webex Calling dial plan · Internal dialing settings · Checked 2026-09-23
54. 54
    The Webex Calling premises dial plan accepts From and To headers in E.164 or as extensions, but not a combination of the two.

    Configure trunks, route groups, and dial plans for Webex Calling · Dial plan section, format requirement note · Checked 2026-09-23
55. 55
    When adding numbers in Webex Calling Control Hub, numbers must be in E.164 format for every country except the United States, where national format is also accepted.

    Manage phone numbers in Control Hub · Add phone numbers section (number format statement) · Checked 2026-09-23
56. 56
    Webex Calling uses E.164 format for calling, connected number identity, outbound call screening and contact resolution.

    Configure dialing behavior for outbound calls · Opening section · Checked 2026-09-23
57. 57
    Webex Calling dial patterns support two wildcards: X for one digit and !, which matches any digit sequence and may appear only once, at the end of an E.164 pattern; X cannot be used mid-number and X and ! cannot be combined in one pattern.

    Configure trunks, route groups, and dial plans for Webex Calling · Dial plan section, wildcard rules · Checked 2026-09-23
58. 58
    For calls resolving to Webex Calling, plus-prefixed E.164 patterns are evaluated first, then enterprise number patterns with no normalisation applied beforehand, and finally domain or URI patterns; where several patterns match, the most specific wins and range patterns using X are preferred over prefix patterns using the exclamation mark.

    Cisco Preferred Architecture for Webex Calling — Design Overview · Patterns and pattern matching, page 30 · Checked 2026-09-04
59. 59
    Phone numbers must follow E.164 format for all countries except the United States, where national format is also accepted.

    Manage phone numbers in Control Hub · Number formatting · Checked 2026-09-04
60. 60
    Cisco states that the outbound dial digit prefix requirement is ignored for outbound calls placed in E.164 format, and that where a national number begins with the same digit as the outbound dial digit the system removes that initial digit, so the outbound dial digit must be added in front of the rest of the national number.

    Configure Webex Calling for your organization · Configure Webex Calling dial plan, step 4, note under External Dialing · Checked 2026-09-15

Documents

Cite this page

WarmTransfer. (2026, September 23). E.164 numbering and dial string normalization. WarmTransfer. https://warmtransfer.net/knowledge/e164-numbering

@misc{warmtransfer-e164-numbering,
  title  = {E.164 numbering and dial string normalization},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/e164-numbering},
  note   = {Verified 2026-09-23}
}