We are about to install a new MA30120 and we want to use a PRI T1. Is it possible to determine which phone number (line) was dialed with PRI?

For every call that Telco sends (via a PRI T1 line) they include the "called number" and the "calling number" (numeric values). This information is communicated via the "call setup" messages within the D channel (ISDN signaling).

For the "Called Number" they will pass along X number of digits (X = variable dictated by their switch/configurable). It might be the last 4 digits or whatever is agreed upon at the time of ordering/installation. This is commonly referred to as DID digits

For the "Calling Number" they usually pass along the full 10 digits of the caller (CallerID info - numeric only).

The MA30120 can utilize this information for delivering faxes that come into us via the PRI line.

The Modem Usage ->Fax Setup>menu is used to do this. Here you can associate an email address to a DID number (called number). This menu is making entries in the FaxDispatch file (/var/spool/hylafax/etc/).

You wrote "....is there a way to get the line or phone number that was dialed", we refer to the dialed number as the called number.