How to make a simple softphone?

[hipokrasi]

Hello, I was wondering if I can make a simple softphone application for windows platform by using a SIP API DLL file so on?
What I am currently using is Autoitscripting language to make applications. So what I exactly need is to call a dll file which allows to use voip sip protocol. Is this possible?

Thanks

 

[jpillow]

Why do you not just use the 3CX softphone or Windows?