CallingCard application (actually simplified - details to be discussed ) made on highly scalable cloud platform, foreseen to serve multithousand concurrent calls.
There is selected solution for origination: professional company (like [login to view URL]), which has access numbers, and directs calls as SIP do defined IP destination ( = CallingCard app ).
There is selected solution for SIP termination: also very pro company with full AAA functionality (Authorisation Authentication Accounting).
Please referr to simple diagram attached.