Skype for Business Certified IP Phones with Microsoft Teams

Ryan Steele MTSBob , by direct network connectivity I mean there's no NAT or firewall inspection between the endpoints. So, if there is - then the calls drop for me. Like, if User 1 is at the office with his 3PIP desk phone, and User 2 calls him from the Teams App on his LTE-connected smartphone from outside.

Sure could be firewall or some other network issue - but are there differences in network requirements between these scenarios?  I'm not aware of any.

Desk phone (User1, migrated to Online, any coexistence mode) <-> SfB client (User2, migrated to Online, Islands or SfB only)  - this works.

Desk phone (User1, migrated to Online, any coexistence mode) <-> Teams client (same User2, migrated to Online, Islands or Teams only) - this doesn't work.