Make Teams call without assigned number

nc-novelt With Microsoft Calling plans will need to have a number assigned, but you can then use a CallerID Policy to replace that, for example with a number for a reception or contact centre if you don't want the direct number shown. Manage caller ID policies in Microsoft Teams - Microsoft Teams | Microsoft Docs

If you are using an SBC then no you don't need an externally routable number, my employer gives a core number with an 'extension' number. I don't care as no one has ever called me on it, I cant quite imagine why they would.

nc-novelt I don't think that is possible. The system must have something to send out for Caller-ID on PSTN.
Here is the link to the MS Docs.  

I have both the PSTN for DID and making & receiving phone calls and also have the Conference Add-on.

I can tell you a little trick to make outgoing calls but if you expect to receive in-bound calls direct it doesn't work.

If you only want to make outbound calls you can purchase Conference Add-on and get the pooled minutes that come with that subscription.  Then when you want to call out, you can use the Add Participants and dial out to a number.  The number that is displayed on Caller-ID is the number of the bridge line.

nc-novelt 

StevenC365?