Also, there's a little hack that you can do to make 5 lines appear on the M7410/T7406/e that will make there be 5 lines + 1 intercom. Connect a M7310 to the port you want to program. The left top 3 keys and the right 3 middle keys are mapped to the handset buttons verbatim. Program these on the M7310 and then connect your base unit. The wireless units emulate an M7310, and the key programming should hold in place.
John Panzer