[HELP]Quintum A800 connected to Asterisk

Hi Folks,
I’m using a Quintum A800 connected to an Asterisk; I need to identify which pbx line originate the call for billing purposes. I couldn’t find in the configuration an individual account for each pbx line. Looks like the A800 only has one sip account for the whole system, so all the PBX lines validate with the same SIP account.
Does anybody know how to identify the PBX line for each originating call?
Thanks in advance.