Salt water is highly conductive and highly corrosive. If the phone was on at the time, it's probably toast. If there is any hope of reviving the phone, you must remove all traces of salt. I wouldn't normally recommend this, but it doesn't sound like you have anything to lose, since the phone is not currently working.
Remove the back cover, and then remove the battery, SIM, and SD card. Pour distilled water over all surfaces of the phone except the speaker area. Shake off what you can, then blast it with canned compressed air. Avoid placing it in direct sunlight, and let it air dry overnight. Burnish the battery, SIM, and SD contacts with a soft pencil eraser, and then reassemble everything. Now try turning it on; it will either work or it won't.
Good luck.
