@skip: It's not for us (we have a "real" phone system). But we encounter small businesses all the time that have some random brand of 2-line or 4-line phones that they bought from OfficeMax/etc. They want MoH but don't necessarily have the finances to upgrade to a "real" phone system. We're not even in the phone business (we're in the fax business), but I've heard this request so many times that I thought I'd do some research and see what was out there.

@dan: The concept of the MP-412 is exactly what I'm looking for, just for other 4-line systems. Of course this one is proprietary and works only with the NSQ412. But thanks for the info.