Having been a part of VoipO since it's Alpha testing days, I've gone through quite a few adapters. Including some of my own. I remember having a grandstream at one time, during beta, but it had an issue. That's when we went to the PAP2. The issues were resolved and the grandstream is good again. I'm still using the PAP2. I was using my RT31P2 for a while because I was moving things around and wanted to gut my system. But I'm back to the PAP2. I do also have SIPDROID running on my Android phone. Works really well when I'm in an area with no cell coverage but I have WIFI.