What to Do:
1) Get it out of water. be very quick. this is the most important step.
2) Take the battery out immediately, if you don't the whole phone will short circuit and die.
3) Take the SIM card out. (memory cards too)
4) Open all possible openings in the phone. (charger slot, memory card slot, etc, etc)
5) If its a slide phone, slide it open. Water trapped in there too.
6) Place it in a dry area and a little bit warm for 24-48 hours. Sunlight is good.
What to not Do:
1) Do not use a hair dryer. that pushes the water further into the phone.
2)If your cell phone fell in salt water, rinse it completely with fresh water before proceeding to the steps mentioned here. The salt can further damage your cell phone and increase the risk of corrosion.
3)Never place the battery near a source of heat. It may explode!
Remember this all a factor of time. Be very quick!