I don't use OBiTalk to configure my OBi's. I only used OBiTalk to configure GV then switched to the local interface. I THINK the dashboard only shows the SP as configured when you use a wizard and not OBI Expert.
The outbound proxy is used for outbound calls. Since we are only receiving calls, I didn't include it in the configuration.
I couldn't get the OBi to register to GetOnSip. I guessed and turned on SRV support, fixing the problem. SRV allows a provider to use 1 or more proxies. They can swap proxies without disrupting their users.
getonsip.com is not the real proxy, but points to another proxy.
To see the real proxy (sip.onsip.com) type the following in the Windows Command Prompt:
nslookup
set type=srv
_sip._udp.getonsip.com
Edit:
I know some softphones include SRV support without having to turn it on. Maybe that is why it's not in their setup.