Usually, peer-to-peer is free. If you know another user on the same provider, you can call.
I don't know how you would test the system without a working number.
The PAP2 device has ports for using a standard telephone handset.
If you want to use a soft phone you don't need the router for VOIP. You do need to purchase minutes or talk peer-to-peer.
If you merely want to use a softphone to try out voip, try Voiceglo or sipphone. Download either and send me your number--- I'll give you a call. (voiceglo is simple and free , sipphone has test numbers for testing.)