I have built a lab with OCSR2 Standard version and CUCM 7. I have tried to create a trunck SIP between the Mediation Server and CUCM7, but when i try to reach an IP Phone registred in CUCM from the MOC, it fails ! I have collect some traces, using Wireshark, and i have a SIP error 503 service unavailable from the CUCM. About the Dial Plan, I used a very simple one ^8(\d{3})$ ..... +8$1.
You may also want to check the inbound calling search space on CUCM to ensure that it conatins the partition that your lines appear in CUCM. Also insure that the trunk is set to accept all digits. CUCM 7.0 is comaptible with E164 and the + sign.