When adding users/extensions, it might be rather useful if we could add more than just one "alternate extension" similar to the way we can add many numbers to each contact assignment. A case where it is especially suited is with voicemail ports. The PBX may report extensions 100-108 on an 8 port voicemail, but for purposes of SMDR, we are only interested in representing this with a single "user" name of "voicemail" since there is no functional difference between any of the eight ports.
I consider this only a low priority refinement suggestion. My workaround is to add all the voicemails as users in Department "Voicemail".