Hi everyone,
I was looking to interface my arduino mega to a simple cellphone. i want to connect the arduino to the speaker or the vibrator pads so that when i call the phone the arduino can sense the current and turn my lights on. how do i connect it to sense the current. All the help will be appreciated.

You could check the speaker voltage on the cell phone when it rings... If it's below 5v just read it on one of the arduino inputs.