In the case of both the small boxes, you've really got an enclosure with one replaceable card in it. The works in the General DataComm one is a SpectraComm 553 CSU/DSU. In the ADC one is an Adtran H2TU-R, which seems to be different from what I expect. I think that you're actually getting a T1 over SDSL, which I guess is the new way to do it, and may explain why the telco isn't keeping an iron fist on it. I think that it looks like SDSL to the telco, but T1 to you. Maybe that's the way all SDSL works? Regardless, after that it all looks straightforward, even if I haven't dealt with that actual CSU/DSU. Chances are you won't ever have to touch either of them more than noticing that an error light is on on one of them when your network's down and then call the telco to fix it.