Besided PortaSIP (a very expensive SIP server) there are a plenty of free ones:
1. SER (SIP Express Router)
3. Brekeke (not really free, I think the free license is up to 100 units).
Yes, Cisco 5300 does support SIP (as a sip UA – user agent) and you need a SIP proxy server in order to do the call routing.
As to your question – how to config the 5300, I will answer you if you answer me the question – how to build a house?