Why not get PortaSIP for free?
All of it’s components are open source anyway, and you can just request all Portaone modifications to it and they must share it with you. Just email Portaone and ask for the source codes of their open source components. If they intend to comply with GNU license agreement they must send it to you. If not, they are pirating GNU which not a good thing these days.
Basically GNU license says that any derived open source product is also open source.
It’s funny no PortaSip customer of Portaone has realised yet that it’s probably perfectly legal to take PortaSip components write the documentation on their own and start selling for half the price portaone sell it.
You can also do the same with sysmaster with their modified GnuGK, but not with their modified asterisk which they license from digium under commercial license.
Between portaone and sysmaster I prefer portaone. Both take open source products and sell it for a hefty price making huge money on other people work. But at least portaone has the decency to contribute some code back to the community (like rtpproxy for SER).