Qwerty Keyboard Phones

How does a cell phone keyboard work?

I want to solder wires to some keys of a cell phone keyboard and operate it using some electronic device. I need to know how I can electronically press a button. What voltage should I expect? Is it continuous or in pulses? Do all buttons have a common wire or it is a matrix?

I think each of them are connected to a chip, where all data is attached.

How To: Attach a KEYBOARD to your CELL PHONE