Answer to: How do I know if my phone has water damage?Bummer on the phone getting rained on. To know if it has water damage, remove the back cover and look just above the battery compartment. There is a 4mm square located there that should be white in color. If it is red or a reddish color, it has been exposed to moisture. You can try and put the phone in a plastic bag with dried rice and seal the bag. Leave it in there for two to three days and see if that removes the moisture and corrects the issues you are experiencing.
Answer to: My phone is stuck in a rebooting loop; what should I do?If you have tried to power cycle the phone and that didn't take care of the problem, try removing the battery using this link. If that didn't solve your problem, then the motherboard might be defective and will need to be replaced. Try following the steps on this link to replace the defective part.
Answer to: Can this phone work on different carrier networks?As a matter of fact it will. You will need to call or visit AT&T and ask them for an Unlock code for that particular phone. If you are still under contract, they may not provide it. If you aren't under any obligation, they should provide it. Once your phone is unlocked it can be used on T-Mobile's network.