||Hacking Asterisk and Rails with RAGI|
"Currently, Gizmo is the most open VoIP client out there"
No Gizmo is not the most open, the most open is OpenWengo, it's fully GPL and only use GPL and LGPL libraries, you just can't get more open and free than that. You can use your account from asterisk and use different services from the clients. Here it is: