Adds an additional 24 programmable buttons. Quality varies but majority are good quality. 

Includes SBM24 Sidecar, Stand, Connection Cable and Mounting Bracket.  Does not include a line cord 

• IP Office 6.0 to 8.1 - Compatible with Avaya 9630, 9630G, 9640, 9640G, 9650, an 9650C IP telephones.  Can add up to 3 SBM24 modules per phone; up to 42 SBM24s per system.
• IP Office 9.0 or higher - Compatible with Avaya 9608, 9608G, 9611G, 9630, 9630G, 9640, 9640G, 9641G, 9650, and 9650C IP telephones.  Can add up to 3 SBM24 modules per phone; up to 42 SBM24s per system.