I have started over using a clean SP4 (deleted then added back in again).
In my router, I have forwarded the appropriate UDP RTP ports 17100-17198 and port 5063.
X_InboundCallRoute is set to the default value of ph.
The OBi was then rebooted.
IPKall is set to forward calls to SIP URI: 123@my_IP_address:5063
When I place a call to my IPKall number I get a busy signal. The phone does not ring on my OBi and I see no blocked packets in my firewall log during the time of call.
I don't know where else to look.