[Serusers] :: The best Softphone ?

Hello, I'm using Xlite v1 and 2 but always having so strange behaviors with SER O.8.12: (direct connection , public ip - to - public ip) - with xlite v1 and/or v2 , when i try to make calls : xlite always send 404 not found to the caller (numbering plan: xxx-xxx-xxxx) - no problem to reach someone with Xlite when I type the login - when i make a call with Mitel 5055 or W. Messenger 5 no problem (vice et versa, both direction) I tried with siemens softphone, good behavior but not user friendly Now the question is , is there any other *free* good softphone for windows or is there anybody facing the same problem and know how to resolve it? regards abdoul