How to port Microsoft Phone System phone numbers between Office 365 Tenants?

In this post I describe and share my experience on how you can port numbers from Microsoft Phone System from one Office 365 source tenant to another Office 365 target tenant. First of all, why should you do this? Well, there are several reasons you might have to port existing phone numbers from a source to a target Office 365 tenant, e.g.

  • company merger and acquisition
  • company segregation
  • other forms of organizational restructure measures and needs
  • technology change requirements (migrate / cutover / move (partially) from a PoC environment to a production environment …)
  • security change requirements

When do you have to port phone numbers?

On the one hand, if one of the above reasons or another reason may apply to your organization. And of course, on the other hand, if your organization and you like to keep the phone numbers to carry on getting calls on these ones. To sum it up,

  • you’ll have to port phone numbers if you rely on Microsoft Phone System Calling Plans and
  • Microsoft is also your PSTN service provider from whom you get your PSTN phone numbers
  • and you might published (to suppliers, customers, partners) and adopted  these phone numbers in your company communication with the outside world … (mail signatures, business cards, …)

Is this difficult to do?

Fortunately it is not.
Still, you have to pay attention to a few things to make the phone number porting a smooth cutover and a success. I recommend to read carefully what’s on the Microsoft Phone System documentation and a blog (see links below). I do not mention here that an Office 365 Tenant-to-Tenant migration might has other challenges you have to cope with. I recommend that you plan it – the whole migration – thoroughly to get it working with a minimal impact to your users.

What numbers can I port?

You can port user and service numbers.

What do I have to do?

As a prerequisite I recommend to set up the destination tenant with the appropriate licenses (e.g. E5 + Calling Plan International + Communication Credits + Audioconf …) to be ready for assignment as soon as the numbers are available in the destination tenant. Don’t forget about setting up Communication Credits.

Besides of all your other Office 365 Tenant-to-Tenant (T2T) migration tasks as your first step please read the blog post from “Porting Cloud PSTN Telephone Numbers Between Office 365“.

What data do I need to submit to the Microsoft PSTN Porting team?

Because it is almost always the same data you need to submit to Microsoft  for a T2T migration I just created an easy to use table which you can copy and  help as a guiding and supporting tool.

DataValue (you need to insert)
O365 source tenant domain name…
O365 source tenant unique identifier
O365 source tenant (porting) PIN
O365 destination tenant domain name …
O365 destination tenant unique identifier
O365 numbers emergency location address (for the numbers) e.g. (Floor, Building,) Street, City, ZIP, Country
Number(s) to be ported from source to destination tenant e.g. +49711xxxxxxx to +49711xxxxxyy
Number type (user vs. service phone numbers?) e.g User
Requested date and time range of port requestion execution e.g. 17/03/2019 10am
Request mail-to [Microsoft PSTN Team, see port request Microsoft page] e.g. Microsoft PSTN Europe Team

What’s next?

After you have submitted the request the Microsoft PSTN Team answers, either with additional questions or a confirmation request. You than need to confirm the port request which enables the Microsoft PSTN Team to port your numbers based on the details of the confirmation mail.

During the porting

  • the numbers will be removed on the source tenant,
  • users will not be able to be called or make a (PSTN) call [inform your users early enough],
  • numbers will show up in the destination tenant.

If you have licenses, numbers ready, congratulations you made it and can now assign the user/service numbers within the target O365 tenant.

Conclusion, opinion and summary

In my opinion porting phone numbers is really a smooth migration part of an Office 365 T2T migration. Recently, I had to port numbers and was really positively surprised how straightforward and smooth it worked. The only thing I really want to note and highlight is that if you should have all your licenses early enough in the destination tenant because in a recent T2T migration the licenses where added/booked quite late and that’s why it took some time till phone numbers could be assigned to users.

Additional Ressources


Phone Number Porting Tenant-2-Tenant

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