I agree with most. But I always try to get in what I feel is most important-
1. You can't fight technology. If the technology is digital---then that's what eventually (if the dollars are right) is what your're going to be using. If a customer wants to save money--he can't be leading edge---but he can't be 20 years behind either. He's got to be mainstream. In telephones---the time for digital systems is NOW--if a change has to be made for other reasons. Don't switch to digital just for digial's sake.
2. Digital means two wires---not 4. A person just by switching to a digital system can DOUBLE the amount of wire in his building. How much is THAT worth? Even in new construction, it really is a good deal to have 2 or 3 times more than what you will need for one phone. There are always add-ons(cordless phones, modems, faxes etc.) Not having to run new cable makes a guy look good.
3. Digital integration of voice mails is very nice. This technology has been very popular for at least 10-12 years now. It's so nice & easy for the customer and tech alike.

Rockford VoIP