How to receive Internet calls through myphon

I have got an Internet phone provided by Binatone which gives an option to receive calls both from land line as well as from PCs by a USB port. But it is made for receiving calls through Freshnet Internet calls only. How can I use it for receiving calls from other providers like Jet calls, PC2phone etc. I am not an expert in computer. I will appreciate if some one can advise me. C.Mani Kenya