One of the things that I'd think I'd be interested in is: cheap.
How inexpensively could this be done - labor wise, licenses and hardware.
Another thing I'd like to
NOT HAPPEN is some unusual caller experience such as <<ringing - long delay or Transfer Hold Music and then ringing again>>. I think that would confuse customers and also why I'd lean away from using a 6160.
Thinking about it this morning, it occurs to me that I could do this with a
Ingate SIParator. Wouldn't even need carrier SIP trunks.
Call come in on a PRI. Strip of X digits add X digits and route to SIParator via SIP trunks. The SIParator filters out the unwanted calls and routes back to the Mitel where the Absorb and Insert in the trunk service form converts it back the the original DID number. In the event the SIParator fails a simple mod to the trunk service form brings everything live again. The SIParator isn't free but not that expensive either.
Could do the same thing with an Astrisk box also I would have to think. Either way, using SIP to do the filtering shouldn't change the caller experience in anyway.
I'll have to play a bit and see what I can do.
Ralph