kwbmitel - keyline or multiline
with all due respect, I think you may not have thought this one out completely.
say you had to choose multi or key for the FIRST and possibly only appearance of a DN.
say the customer wanted to set up a complaint or inquiry DID. they expected 3 calls a month so only wanted one key on one phone and an associated mailbox. you made it a multi, thinking that growth would be a second key on the same phone. 3 months later, they asked for another key on a second phone, but wanted the ability to simply put it on hold on one phone and pick it up on the other. they still only wanted one call at a time. you would have to delete the m/w key, delete the DN, reprogram it as a multi, reprogram the m/w and then reprogramm the call rerouting.
then perhaps they have a product recall and want to have 3 appearances on both phones and you have to delete it all again to turn them into multi's. After 3 weeks when the calls die down, they want it put back again.