Water Damage

As soon as possible after this place the phone into some clean water, preferably some kind of pure water. If the phone was dropped into salt water, immediately rinse the phone thoroughly in clean water then place the phone into the water. Do not place the battery in the water, consider replacing it or at least dry it out thoroughly with a hair drier.

Next step is to disassemble the phone OR take it to a service centre depending on your skills.

Completely disassemble the phone and clean each part again in water. Dry the parts with a hair drier and leave at least 24 hours in a warm area to get rid of any water built up under IC's etc. Shake the parts a few times in this period and also attack them with the hair drier again.

Check the phone for corrosion etc, if there's none you may be ok. If there's corrosion you really need to remove it, there are many PCB cleaning products on the market for this sort of work. Check with your local electronics store.

Next step is to carefully reassemble the phone. Use a new battery if available or borrow one. Using the battery that was soaked is not recommended but normally works ok.

All going well the phone still works, if not pull it apart and check that it was assembled properly. If still no go, dry it again with the hair drier and leave for another 24 hours to make sure that it's really dry. In most cases the phone will still work.