Nortel M522 - 22 Button Addon:
The M522 Meridian Mate Expansion Module is compatible with both the M5216 and M5316. The M522 is a 22-button expansion unit, with associated LCD indicators, providing additional keys for lines or features. Up to two expansions can be used, for a total of 44 extra programmable buttons. Combined with Meridian Digital Centrex, the M522 offers effective mini-console capabilities.