One of the things that comes to mind is the need to distinguish between various kinds of VoIP. By way of example, I'm currently using two "VoIP" systems in my office. One is my desk phone -- a cisco-supplied "IP Phone" that is in effect indistinguishable from my previous "hard line" phone. The other is a "software phone" -- Skype on my laptop. Both have a "phone number" reachable by any phone, and the person calling probably does not know they they are getting to be by VoIP. One is fairly fixed in location (it is only usable on my desk) while the other is portable (where ever my laptop has a network connection). One has chat and file sharing while the other does not.
Based on the description of what you are interested in, it sounds like you are tending towards the latter. That may be intentional and/or it may become a source of confusion for those that pick up your LTR.
Peter Murray http://www.pandc.org/peter/work/
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