habreu wrote:
1) Are DID numbers (or DID number channels) the usual solution to handle simultaneous calls in a setup like the one described above?
Yes, but beware that some DID suppliers charge extortionate rates for multiple channels.
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2) Can DID numbers be created from my PIAF based system (from the DID section in a2billing)? Or should I buy them from DID providers and route them somehow to my PBX?
You can't 'create' a DID. They are allocated to you by telcos. So yes, you'll need to enlist the services of a DID provider.
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3) If DID numbers can handle my local incoming calls in this setup, does it mean that my TDM400P and analog lines are not needed?
If you have your DIDs delivered to you via VoIP, then you no longer need the Digium card.
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If so, will they work if I wanted to do some US termination services in the future?
Of course. Just create a trunk in A2B and modify your rate cards to send the applicable numbers to this trunk.
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4) Will international DID numbers allow my potential customers outside of the US to call the US using the setup described above
Yes, you can purchase as many DIDs in as many territories as you like and have them all answer with A2B's IVR. You can even add an additional per-minute charge for each DID if you so desire.