Applies To

Call2Teams Customers



Microsoft Teams processes phone numbers in E.164 format, however many PBX and Trunks use their own dialing plan. 

We offer the ability to convert inbound and outbound phone numbers to and from E.164 as required. 

By default, all phone numbers longer than six digits which originate from Microsoft Teams are in E.164 format. 

All phone numbers that are equal to or shorter than six digits are treated as extension numbers and so no conversion rules are applied to them.

Setting the correct number format is very important, as without this calls may not route correctly.

Potential Issues:

  • For inbound calls (calls in to Teams) if the phone numbers have the wrong format configured, the service might not respond to the INVITE at all, or may return a 403 Error: “No match for service user part”. 
  • For outbound (calls out from Teams) if the phone numbers have the wrong format configured the PBX/trunk may return a 404 Not Found error, as it does not recognize the number, nor how to route the number onward.

What is E.164?

E.164 is an ITU-T recommendation, titled The International Public Telecommunication Numbering Plan, that defines a numbering plan for the world-wide Public Switched Telephone Network (PSTN) and some other data networks. 

It defines a general format for International Telephone Numbers. 

E.164 formatted numbers follow the format:

[+][country code][area code][local phone number]



What are the portal E.164 Number Formats?

If the PBX or trunk is sending numbers in a non-E.164 format then the system will convert these to E.164 before passing on the call to Microsoft.

We offer three different options for our customers depending on their PBX or Trunk configuration requirements:

  • "E.164 with +"
  • "E.164 without +"
  • "Localized"

These are available from the Services page in the portal. Navigate to the respective PBX or Trunk tab as appropriate.



Setup Tip: If users are unable to make or receive calls and are completing setup for the first time, it is worth checking if the number format is set correctly and if it matches to the PBX leg of the call. 


E.164 with +

Selecting "E.164 with +" tells the platform that all inbound calls will be in E.164 format with a leading plus sign (as defined above). 

With this in place we pass the calls on through to our routing engine unchanged. 

For example, if the following number: +1 3225 012 013 is sent into the platform, this would be passed through to Teams as-is.

For outbound calls, Teams will automatically convert numbers to E.164 format before they reach the platform. We will then pass these onwards unchanged.


E.164 without +

Selecting "E.164 without +" means that the PBX/trunk is sending phone numbers in E.164 format without a leading plus sign. For example, if the following number: 1 3225 012 013 is sent into the platform, we will append a '+' to the front of the number and then pass it on to Teams.

For outbound calls, Teams will automatically convert numbers to E.164 before they reach the platform. We will then remove the '+' and pass the numbers onwards.



The Localized option allows granular control over the number format:

  • The outbound fields impact those calls egressing out of Teams. 
  • The inbound calls impact calls from the PBX/Trunk towards Teams.
  • The national fields impact calls placed within the same country. 


Each PBX or Trunk is configured with a country. 

Since all calls originating from Teams are in E.164 format, we can detect if the call is for a target number within the same country.

For example, if the Trunk is configured for California, USA (E.164 country code prefix "+1"), and the dialed number starts "+1..." the system will recognize this is as a within country and apply the National rules.

Further Examples:

Inbound International calls:

A trunk based in the UK, (E.164 country code prefix "44") uses the format 00441234512123. 

In this case the Inbound International Prefix field should be configured with "00". 

This tells the system that "00" is the prefix to remove in order to get the [country-code] and [base-number].

The 00 is removed to give 441234512123

A plus sign + is added to give +441234512123, which makes the phone number E.164 format. 

The phone number can then be passed on to Teams.

Inbound National calls:

A trunk is based in the UK, (E.164 country code prefix "+44"). 

Inbound calls within the UK might arrive without any country prefix; for example 01225 012013.

To correctly handle this, the Localized option must be used, and the Inbound National Prefix field should be set to "0". 

This tells the system that '0' is the prefix to remove to get the [base-number]. 

The system can then add +[country-code]. 

The system uses the [country-code] from the trunk/pbx configuration.

01225012013 is converted to 1225012013, then the PBX/trunk country and a plus sign are added to give +441225012013 which makes the phone number E.164 format.

Note: Some trunks may use the international format for phone numbers within same country as said trunk. This is fine.

Outbound International calls:

The dialed number from Teams will be in E.164 format. 

For this rule to trigger the country code for the dialed number must be different to country code configured on the PBX/trunk.

For example, if a trunk is configured to be based in the United States (E.164 country code prefix "+1") and a UK number (E.164 country code prefix "+44") is dialed then the rule will apply.

+441225012013 is called from Teams. 

The leading plus sign is removed. 

The "44" is kept.

"00" is added to give 00441225012013

Note: As stated, the phone number called will originate in E.164 format. If the number has a different country code to that of the PBX/Trunk only the plus sign is replaced, using the Outbound International Prefix field value "00".

For Outbound National calls:

If the number dialed is in the same country as the trunk/PBX configuration then both the '+' and the country code are removed.

For example, for a UK trunk, if the number dialed matches "+44" then those characters are replaced with the Outbound National Prefix field value of "0".

+441225012013 is dialed from Teams. The leading "+44" is removed and "0" is added to make 01225012013.


10D dialing (Only for North American (US/Canada) customers)

If users need to dial a number without the leading "1" or "+1", then E.164 rules can be created to format this for Teams, as shown below.

Similarly, if the service provider presents numbers without a leading "1" or "+1" then the E.164 rules below will add the "+1".