To use the OBiTalk network for routing calls, the OBi100 must be added to OBiTalk. It doesn't take much effort to add the OBi100 back to OBiTalk.
There is another method that routes calls over your local network that doesn't have this requirement. You can do the configuration from the OBi100's local interface. It's a little harder setup, but it's a better solution. You're not dependent on the OBiTalk network. It's a similar setup except you need to define a dummy trunk on each box to do the routing.
It's your call on what method you want to use.