What is your PSTN connection you are planning to use Analog, digital, and how many circuits. There a some gateways out there that will do the job very reliably however if you want to do prepaid calling card services there are only a few that do it successfully and willing to change as the telecom market changes. The IVR portion for Cisco or Quintum, is typically a TFTP Server prompt storage server for multiple languages and the RADIUS Server tells the TFTP Server or if the prompt is already cached in the gateway’s memory will play the proper prompt to the enduser. Look at Quintum, they are a true voice gateway with true RADIUS Attributes dedicated to voice networks and voice and billing attributes for the various billing needs a Dialogic could also give you, where as like Cisco they are more into the data networks, and the radius is designed more to work with data networks not voice. Cisco is a great gateway don’t get me wrong, but from here what you have to look at is the billing and IVR system needed to do calling card services through a VoIP network. Today there is no need to buy Dialogic platforms unless you want to do more of a unified messaging system. That too is being changed with various IP messaging platforms coming into the market place at a much lower cost than the legacy Dialogic switches. There are Dialogic switches in the market that can handle typically 16 T-1’s or E-1’s then to scale you have to build another. The billing on Dialogic is usually charged on a per port basis which can be extremely pricey.
Doing a RADIUS build with the proper radius server array you can handle more than 20 million but there are not many systems on the market than go past 10 million minutes per month. Post your e-mail and I can discuss more.
Low entry and quick ROI now adays with either a hosted solution or owning your own.