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Medium restriction for Call Handling & Forwarding: BYOP number seen as external



We've a BYOP integration during our migration stage in order to permit short numbering between Zoom phone and our current phone system. Everything is working except for the forwarding.


Indeed, we don't allow external forward, so we've checked in Call Handling & Forwarding => Medium restriction (external numbers and external contacts not allowed).

=> The issue is BYOP numbers are seen by Zoom as external numbers instead of onnet internal number.


What is the solution in this case ?


Community Champion | Zoom Partner
Community Champion | Zoom Partner

hi mpecc41,


You will need a session border controller (sbc) to connect your on premise pbx to zoom phone.  Calls made from zoom phone to your on premise pbx need to be routed to the sbc instead of being forwarded and vice versa.


Zoom has certified the following Session Border Controllers:







Zoom Phone Certified Hardware


I suggest discussing with your zoom account team and possibly with zoom professional services.


Depending on the number of sites, their locations, the number of existing carriers and the number of users, you may want to consider other alternatives.  With the help of zoom professional services, we migrated 400 users from an avaya ip office pbx to zoom phone all at the same time.  There were over 30 sites in two states and 5 carriers.  On the port date, the old avaya phones stopped ringing and the new poly vvx desk phones connected to zoom phone started ringing.  No lost calls.  There were no issues.


Did my response answer your question? If so, please don't forget to mark the reply as an accepted solution.


thanks,  eliot


Hi Eliot,


We've already Cisco SBC interconnexion (BYOC for PSTN call / BYOP for internal calls on short numbering) with Zoom phone : calls between them are working fine. 

Our migration can't be done in one shot because we've a lot of sites and users (several thousand) so during this time, some users will be on Zoom phone and some on Cisco. 

And some users should be able to enable permament forward via short number between the two world. On Cisco side, no issue, we've the granular option to do that but on Zoom, Call forwarding option are very limited. In my own comprehension, BYOP (Bring Your Own PBX) is here to allow internal call (no need e164 format), so why in this case, Zoom consider these number as external instead of internal ?




We've PSO and he asked us to submit feature request, either to improve call forwarding granularity, or change BYOP call classification.


If you have another solution, I'm aware 🙂



Community Champion | Zoom Partner
Community Champion | Zoom Partner

hi mpecc41,


in addition to zoom pso, you might contact your zoom account executive and his/her se for any suggestions they may have.


also, consider contacting cisco sbc support.


finally, another possible approach is to use a shared directory of external contacts.

Creating a shared directory of external contacts (

This feature can be useful in these scenarios:

  • When migrating a large number of users to Zoom Phone, you can migrate a portion of your users, then import the contacts that are waiting to be migrated. 

thanks,  eliot