Provides 24 additional lines for incoming calls, outgoing calls, and calling featuresNo separate power supply needed. However, using more than one button module changes the power class of the phone to Class 3IP 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.Avaya Communication Manager R4.0 or higher - Can add up to 3 SBM24 modules per phoneAvaya Communication Manager below R4.0 - Support for one SBM24 per phone