Law number one in Quintum prepaid aplication:
1) You could go from PSTN to VOIP (network side)
2) You could go from VOIP to PSTN or PBX
3) You could have a IVR answering calls on the PSTN side
4) You COULD NOT go from VOIP to IVR.
Again, if your call comes via network, you could not tell quintum to pick it up and play an IVR.
At least you could not do with a clean solution, with good quality and good levels.
What some people will do is “loop” the PBX ports to the PSTN ports , and get the PSTN ports to answer and play the IVR.
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