EFM (Ethernet in the First Mile) is going to come in on an IAD (Integrated Access Device) probably manufactured by Adtran or Cisco. It will deliver your PRI and your Internet access over the same circuit, the Internet bandwidth will be dynamic, depending on the number of Voice channels in use at any particular time.
Since it will be some type of VoIP transport back to their CO switch, you will probably have difficulties with devices like Faxes, Modem, Credit-Card readers, etc., and may need to force them to communicate a slower speeds. If you use WinSPM for remote programming, it would be a good idea to keep at least one POTS line connected, as well as perhaps some for fail-over and fire/burglar alarms.