This example assumes you want to be able to make calls between OBi devices using SIP. The OBi devices reside on the same network and have the following IP addresses: OBi-A @ 10.10.10.2 & OBi-B @ 10.10.10.3
You may use this same configuration methodology with any SIP standard based VoIP endpoint.
Configure the OBi devices using the integrated web UI or the OBiTALK OBi Expert pages:

OBi-A Configuration:
A. ITSP Profile A -> SIP proxy = 10.10.10.100 (or any IP address in the subnet)
B. Voice Services -> SP1 Service
1. Un-check: "X_RegisterEnable"
2. AuthUserName = 2222
C. User Settings -> Speed Dials
1. SpeedDial 2 = **13333@10.10.10.3
the attached telephone.

OBi-B Configuration:
A. ITSP Profile A -> SIP proxy = 10.10.10.100 (or any IP address in the subnet)
B. Voice Services -> SP1 Service
1. Un-check: "X_RegisterEnable"
2. AuthUserName = 3333
C. User Settings -> Speed Dials
1. SpeedDial 3 = **12222@10.10.10.2
To call OBi-A, press 3# from the attached telephone