best voip solution for porting would be Twinklephone!!! This is a VERY powerful tool and would be more than worth the effort...
http://www.xs4all.nl/~mfnboer/twinkle/download.html
In addition to making basic voice calls Twinkle provides you the following features:
2 call appearances (lines)
Multiple active call identities
Custom ring tones
Call Waiting
Call Hold
3-way conference calling
Mute
Call redirection on demand
Call redirection unconditional
Call redirection when busy
Call redirection no answer
Reject call redirection request
Blind call transfer
Call transfer with consultation (attended call transfer)
Reject call transfer request
Call reject
Repeat last call
Do not disturb
Auto answer
Message Waiting Inidication
Voice mail speed dial
User defineable scripts triggered on call events
E.g. to implement selective call reject or distinctive ringing
RFC 2833 DTMF events
Inband DTMF
Out-of-band DTMF (SIP INFO)
STUN support for NAT traversal
Send NAT keep alive packets when using STUN
NAT traversal through static provisioning
Persistent TCP connections for NAT traversal (new)
Missed call indication
History of call detail records for incoming, outgoing, successful and missed calls
DNS SRV support
Automatic failover to an alternate server if a server is unavailable
Other programs can originate a SIP call via Twinkle, e.g. call from address book
System tray icon
System tray menu to quickly originate and answer calls while Twinkle stays hidden
User defineable number conversion rules
Simple address book
Support for UDP and TCP as transport for SIP
Presence
Instant messaging
Simple file transfer with instant message (new)
Instant message composition indication (new)