It’s possible in Teams and in Entra ID/AD phone number fields to use whatever number format you wish and have things sorta kinda mostly work (at least internally). Your mileage will vary when you need to interact with the outside world, and things will just get messy if you are an international organization.

The source of this problem is assumptions. A user might assume that any 10 digit number is a North American phone number because that’s what North American phone numbers look like to North Americans. What about other countries with phone numbers that might also be 10 digits long? I might write (604) 464 2214 for a phone number in Vancouver, BC. A user in Malaysia might write 60 4-641 2214 for the Penang airport. Houston, we have a problem!

If a user clicks on these phone numbers in most Microsoft apps and most web browsers, their local dialing rules will usually be applied. That’s fine, sort of, if your users will never ever call another country, but will quickly lead to frustration if they have to.

It is imperative that international organizations use E.164 format in Entra ID and/or Active Directory. Everybody else should too, especially if there’s the tiniest chance that the organization will expand to a second country. Even a sales person or liaison in the UK from a US organization counts!

How does E.164 help? First, it requires that the country code be included at the start of the number. That would at least give us 1 604 641 2214 for the Vancouver number, with 60 4-641 2214 have 60, the country code for Malaysia. This doesn’t get us entirely in to the clear, as we still can’t tell whether the first digits are a country code or an area code within some unknown country. Prefixing the number with a + symbol indicates that the number does indeed start with the country code. That gives us +16046412214 and +604612214, guaranteed to be globally unique.

A common source of “assumed” formatting with numbers in AD/Entra ID is 3rd party systems like HR applications that push employee information into the directory. I’ve come across systems that are old enough and/or poorly written that just can’t do anything other than “well everything MUST be a US phone number!”. I’ve also come across organizations where HR inputs numbers in whatever format, because they aren’t thinking about click-to-call and what’s going to happen with the number after they type it in during the employee’s onboarding.

And finally, if you are find yourself mad at Teams because the user’s phone number doesn’t show in their contact card, and you have to go and enter these numbers in to AD/Entra ID, stop! Teams purposely doesn’t display the Teams phone number in contact cards because it’s not necessary. You can call another user in your organization by clicking on the phone icon in all of those drop downs. You don’t need to click on a number for a Teams-to-Teams call!