You can find this in admin guide:
Speed Dial Numbers
Each OBi device supports 99 speed dial numbers. The 99 speed dial slots are numbered from 1 to 99 and are invoked by dialing a 1 or 2-digit number corresponding to the slot number. Speed dials may be dialed from the PHONE Port or via the Auto Attendant. Note that the 2-digit numbers "01", "02", ..., "09" are not admissible; you must dial the 1-digit number "1", "2", ..., "9" for slot number 1-9.