BCM CMB4x16 Combo Media Bay Trunk Module:

Nortel NT5B42AAAFE5 Business Communication Manager 4 Port Calling Line ID Trunk Media Bay Module Combined with 16 Port Digital Station Module for the BCM 50, 200, 400 and 450.

The Nortel BCM 4x16 Combo 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