Teams Business Voice and extensions

New Contributor

I am looking for some assistance if anyone can help out.


I am migrating our existing phone system to Business Voice and I am running into some issues getting extensions used how they used to be. Basically we have our main number (ex. 123456789) and I would like to be able to dial externally then input the extension (ex. 115) and reach that user. And internally just dial another users extension to reach them.


Here are a few specific things I am running into


Our auto attendant is set to dial by extension but I cant actually get it to route to a users extension

We have the users Office number field in Azure and O365 as 123456789;ext=115


For internal extensions I am looking for a way - maybe through dial plans? to get the input of the extension to go to the user as well. Note our auto attendant number and user numbers are separate meaning they extensions are not part of the main number in any way (1234567115) where we could just cut off part of the number.


Any advice would be greatly appreciated.

6 Replies



If you want to use Extension calling from an Auto Attendant it is the format +123456789;ext=789 you have to use.

Set up an auto attendant for Microsoft Teams - Microsoft Teams | Microsoft Docs


From a Teams client it is better to learn users how to call by name, ex. "/call <name>". But I guess you have desk phones that you want to use extension calling from, then in your Dial Plan you can setup this. But the extension have to match the number, so +123456789 would have extension 6789.

Use Extension Dialing in Microsoft Teams (

Thanks for the reply, internal extensions are quite as big of a deal if we just use contacts to call but do you have any recommendations for external callers reaching users via extension?

Not sure if you still need this, but in my case, I am utilizing unused -MobilePhone ext. (You will be required to install MSOnline module):


$cred = Get-Credential
Connect-Msolservice -Credential $cred
Set-MsolUser -MobilePhone ext=1001 -UserPrincipalName user@domain.tld

This way, user@domain.tld can be reached through Auto Attendant by dialling 1001, given the Auto Attendant setting is set to reach user by number.


Not sure if your query was answered. But the external people can call the Auto Attendant and then dial by Extension Feature to the reach the users via extension.

With Regards,
Satish U


Just a brief FYI to advise that this *does* work, but that you have to give Microsoft's back-end some time to process.  Additionally, I was able to add the ext=#### by simply logging into the M355 admin account and adding the information I needed in the field.  Again, it look some time for Microsoft to apply those changes, so be patient.

I can also confirm that while it does work on the "dial by extension" setting in Auto Attendant, it doesn't seem to work for dialing numbers internally.

A question: In the company where I work, the use of 7-digit extensions (XXXXXXX) is required. Is it possible to implement this range? For example: phone number "+34YYYYYYYYY;ext=XXXXXXX.
Thanks for your reply.