How could i use blue tooth or a cell phone to remotely operate a 20 amp 110v switch, like a light switch?

That's deviCe.
X10 is no use to you.
A telephone answering machine could be adapted to receive your call from a cell phone. You can then send a DTMF code to a decoder connected to the answering machine, to do your switching. To confirm the desired action has occurred, a tone could then be sent back to you. A different tone could be used to distinguish on from off.
The DTMF code can just be a number you press in after the machine answers. The cell phone generates DTMF.
Without some sort of security, anyone calling your home number could activate your switch unintentionally. There would have to be a disconnect timer at your home, just in case.
Remember, anything connected to a telephone line must comply with regulations.
There could be commercial remote control units available, if you enquire. The cost could save you a lot of hassle, and possible unreliability.