If they want to use the 3CX has PSTN connector Teams (they call it SBCs), it won't work, I tried. You need a certified SBC that simply takes the Teams call and put it on old phone wires.All I know at this point is they want to integrate with Teams. I will find out further tomorrow.
Check this:Any recommendations for headsets that work well with the APP?
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.