Unable to assign telephone extension number to Teams user with Set-CSOnlineVoiceUser

Those of you that are familiar with using the Set-CsOnlineVoiceUser cmdlet to set users telephone numbers in Teams may run into the following issue if you’re trying to assign an extension number to a user:

example:

Set-CsOnlineVoiceUser -identity craig@chiffers.com -telephonenumber “tel:+61281234567;ext=5110”

set-csonlinevoiceuser : The input of parameter “tel:+61281234567;ext=5110” is not in a valid format. Please provide an input
with an acceptable format <tel:>+[number]”, e.g. tel:+18005551234 or +14251234567.
At line:1 char:1
+ set-csonlinevoiceuser -Identity craig@chiffers.com -TelephoneNumber ” …
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Set-CsOnlineVoiceUser], BvdCmdletException
+ FullyQualifiedErrorId : TelephoneNumberInvalidFormat,Microsoft.Rtc.Management.Hosted.Bvd.SetVoiceUserCmdlet

The reason for this is that the Set-CsOnlineVoiceUser cmdlet is being deprecated, and will be replaced with a new cmdlet (that’s currently in preview):

Set-CsPhoneNumberAssignment

Using this new cmdlet, you can assign phone numbers along with extensions to your voice users, regardless of if they’re direct routing, operator connect or a Microsoft Calling Plan.

Set-CsPhoneNumberAssignment -Identity craig@chiffers.com -PhoneNumber “+61281234567;ext=5110” -PhoneNumberType directrouting

Microsoft have published further details on the new cmdlet here: Set-CsPhoneNumberAssignment (MicrosoftTeamsPowerShell) | Microsoft Docs