According to your problem I would say that you did not configure either your Network Conection in the PSP or the security settings in your router (or both) properly.
If you see the next error mssage
"sceNetApctlConnect returns 80110601", proceeed as described
HERE.
But bear in mind that quoted from the Readme.html instructions file enclosed in the package:
(...)
Note that we were unable to get the SIP Phone working with voipbuster.com.
(...)
VoIPBuster, VoIPStunt, VOIPCheap and so many others are exactly the same company.
There´s people who got it working though but do not expect it to be amazingwith those SIP providers.