If you are in a location where you could get E1 or T1 lines, do not go analog.
Get one of the digital systems instead.
If you could only get analog phone lines, like Mike said, you have to decide the configuration first.
If you will have customers dialing into the Quintum, via analog phone lines, you need the one with FXO interface.
If the Quintum will be connected directly to PHONES, like in a call shop operation, or call center, where the people making the calls and the Quintum are on the same location, you will need the FXS type.