I have a customer that opted to go with a 4-digit numbering scheme, rather than a 5-digit and they have nearly depleted the available non-DID extensions for an upcoming phase of rolling out CER. They want to do approximately 1300 ERLs (zones) and have secured a DID number from the carrier to assign to each zone. The problem I have is this. I need to assign a number for the router pattern to integrate UC Manager with CER for each ERL and there are no contiguous number ranges left to use. I talked about the option of using their new DIDs and prepending a digit string such as "01" or "021" or something that would be the LEAST likely to already be used as part of the current dial plan and add NEW partitions to this number range to prevent anyone from inadvertently calling this number range from an end user phone. Does this seem like a feasible design alternative and what are the impact issues as far as interaction with CER, that I should be aware of?