It's not just limited to the PM2e, and also, simply having digital wiring
(T1/DS1, PRI, etc.) won't necessarily do the trick even if you do have
digital modems (PM3, Ascend Max, etc.) There can only be one A/D
conversion and that's at the phone company's central office. Even if you
have T1's coming into the building, it doesn't mean that all of the
signaling between you and the central office is digital. The only analog
signaling that can occur with X2 or K56Flex is between the end-users modem
and the phone company. From that point on, the signaling must be 100%
The above isn't contradicting what John Miller said; it's just simply
adding to it...
I don't really have much of a recommendation as to which 56k
interim-standard to use. The K56Flex is in more modem manufacturers'
modems, while USRobotics sells more end-user modems in the world than
anyone else. In the long run, it probably won't matter which way you go,
because any upgrades from X2 and/or K56Flex to the ITU-T's standard
(if/whenever it comes out) will more than likely be free anyway (unless
physical upgrades are necessary).
We have an Ascend Max 4004 (using Rockwell-based chipsets), so we'll be
K56Flex when the new modem cards come in. Personally, I'm still using the
rock-solid USRobotics Sportster 33.6 (upgradeable to X2). I haven't
upgraded mine to X2, nor am I planning to anytime soon. I do have a second
modem in my machine that I also use when dialing up using MP (Multilink
Protocol) with Win95/NT. This modem is a Hayes Accura 56k (K56Flex) and
that modem seems pretty nice too.