The present invention discloses a method to operate phone using a single key, first provide method to form ‘key value’: (1) When the key is just closed, plus 1 to the ‘key value’, (2) When the key closing time is greater than time t1, form ‘closing key value’, (3) When the key closing time is smaller than t1 and the immediate key releasing time is greater than t2, store the key value as ‘releasing key value’, (4) When the key closing time is smaller than t1 and the immediate key releasing time is smaller than t2, skip to step (1). The ‘releasing key values’ can be used to represent the numerical and alphabetical keys on typical keypad of phone, while the ‘closing key values’ can be used to represent the function key on typical keypad of phone, so that the complete function of a typical phone keypad can be realized using only one key. Therefore, a phone can be made very small, which can be especially useful when installed on small Bluetooth device that connects to phone, since not only can it answer incoming phone calls, but also making outgoing phone calls.