Nortel BCM GATM4 Like New Features The global analog trunk media bay module (GATM4) provides an interface for four analog public switched telephone network (PSTN) lines Supports both pulse and tone dialing, as well as caller ID and disconnect supervision in selected markets throughout the world Compatibility The Nortel BCM GATM4 is compatible with the BCM 200/400 Main Unit, BCM 400 Expansion Unit, BCM 450 Main Unit, BCM 450 Expansion Unit and BCM 50 Expansion Unit