M3902 has a hard key on the display that is labeled "Transfer". While a call is in process, you press the "Transfer" key, dial the number you wish to transfer to, and press the "Transfer" key again. M3903 and M3904 have a soft key on the display that will say "Transfer" when a call is in progress. You press the key below the word "Transfer", dial the number you wish it to transfer to, and the display will now show "Connect". You then push the key below the display that says "Connect" and your call will be transferred.