We have the Newbridge 3624's in service and they seem to work well. We
had some initial install problems with grounding and the t1 quality but
those seem to be resolved now.
Assuming the t1 quality is good the connect quality should be very
good as well.
If your t1 is "too long", has "too many repeaters", or "too many echo
cancellers" then the audio quality will be poor. This is the case even
though the lines are "digital".
Regards,
Mark Hittinger
bugs@win.net