Digital Tenors like D800/D1600/D3000 and newer DX units can connect to either T1 or E1 (software config) and can use either ISDN or CAS signaling like E&M or R2.
Analog Tenors like A400/A800, AX and AS can connect to normal analog phone lines and to normal analog phones as well as analog ports from a PBX. Analog tenors cannot use ISDN, only analog.
There is also a BX tenor that is for BRI ISDN.
If you need more help, you can contact me directly at mike_voip@hotmail.com