Avaya IP Office Installation Manual page 330

The maximum number of simultaneous TAPI WAV user calls
and voicemail users is determined by the IP Office control unit
type; Small Office Edition = 10, IP406 = 20, IP412 = 30,
IP500 = 40 (IP Office 5.0+) / 30 (pre-IP Office 5.0).
IP Office Installation
IP Office
System Components: Applications
15-601042 Issue 20b (16 July 2009)
Page 329