SIP message manipulation

Hi,

My name is Thomas (21), I am student of computer engineering. Task at my school was to make a program that changing original SIP/SDP messages when using VoIP.

The task was hard, I admit to find help on the internet. I found SIP SDK that do the same. Check out if you like:
http://www.voip-sip-sdk.com/p_223-si...mple-voip.html

Think that was great. But somehow I has to change it a little not to look like cheating. According to program (SIP SDK), can you giving me advice on this?

Or other ideas are welcome also.

Greetings to everyone