Hi Khurram,
Are you referring to internal SIP trunking (internal call plan) or are you referring to public PSTN SIP trunking?
I believe there are a few documents on Nortel's site that I can probably dig up for you. With respect to the licensing I'm not really sure with the BCM since I primarily use the SRG (same hardware different license/software configuration).
I'll see if I can dig up any of those documents for you, perhaps you already have them?
Cheers!