I think that GPRS traffic is not counted as “Erlang” in CS traffic report due to this argumentation based on Alcatel Stats:
1) Fixed PDCH timeslots are never taken into account for allocation for voice traffic.
So Max Busy TCH in One Hour = Always Number TCH defined (including PDCH timeslots) – Number fixed PDCH.
2) On A interface, Reports on CS traffic always shows GPRS CIC (s) as Idle even when GPRS traffic was done.
3) When evalutating interference with Idle channel Measurements,idle PDCH timeslots are never taken into account.