The Iphone, like any piece of electronic equipment, may be irreparable after submersion. However, there is a process in which this can be determined.
Make sure you have removed the battery. Also, remove the sim card and "break down" (unscrew, dismantle) any other parts that you can.
Fill 3 ziploc bags with white rice. Place the assortment of parts, keeping the battery completely seperate from all others, in the rice bags. Let sit for 2-3 days.
Placing the components (screen down) in the sun on a table for a day or so after might also be a good idea.
A hairdryer alone wont do the trick and you may spend a few days without phone, but this process may work for you and save you a few hundred dollars.