Softphone

hello,
i want to make a my own software program with vb.net.
could you help me where i can start?
i cannot make connection to sip server with my vb project? i don’t know how could do that.
is here any api or lib for vb.net if possible could you send a link
thank you

This is a duplicate of a recent thread with the same subject. The advice was, read all the relevant specifications and learn C.