DP720/750 dial plan issue


I have a distributed centralized corporate directory accessed via LDAP. It is centralized in that the same directory is shared between all offices and distributed in that it is replicated to all offices.

As such, every non-extension phone number in the directory is prefixed with a plus (+) sign. The individual asterisk servers handle the + where necessary and cell phones handle it anyway.

All other phones happily send the + to asterisk, however, the DP720/750 reject the call locally. This appears to be specifically as a result of the + sign, which has been recognized as a valid digit in phone numbers for years, meaning ‘exit prefix’.

This can’t be changed in the directory as, while the same world uses 00 as it’s exit code, North America uses 011, so the phone has to pass the + to the PBX for handling.

How do I get the phone to accept the + as a valid digit?