SIMPLE? Depends on your definition of the word...
You can check around on this site, especially on the Home page for various articles, opinions and white papers on the different systems available to you.
I'm Nortel biased, and from what you described, I would suggest a small scale 11c (one cabinet should do ya for now) and go with that t1 the phone co. want's to sell you. It would offer up a lot of features the Merlin has as well as being able to be expanded. Another Nortel option would be a Norstar, which is similar to the Merlin you're currently using (at least that's been my experience).
Both you should be able to find a good vendor for on the web, or even Ebay! (I know of a guy in the Dallas area that's selling a system and will even install it for you)
Good luck....
Anyone else have a suggestion?
PG
__________________
You can't wield supreme executive power just because some watery tart threw a sword at you - Look, if I went 'round saying I was an Emperor, just because some moistened bint had lobbed a scimitar at me, they'd put me away!