I will release a SIP client beta 1 for the Blackberry in a few weeks.
1) It only works on GSM phones
2) It only supports G.711 codec
3) Eventhough it works on OTA and WIFI, it would be locked for WIFI only
4) STUN server address is hard coded in
5) DTMF relay has not been implemented
6) The outbound proxy is the same as the registration server
7) It will have an expiration date of 7/31/10 (could be changed)
Notes: We have tested this on no less than half a dozen commercial servers and all of them checked out.