How many times do you power cycle your phone? Seriously now. Just like rebooting your computer will usually fix many problems. The same can be said for your cellphone. Try power cycling your phone every other day as the phone does recieve updates periodically.
Buy T6 tool from Sears. Use fine sewing pin to pop out the two screw covers on the back. Remove battery and SIM card. Remove antenna. Remove 4 screws. Easily run your finger nail along the edge and open the back. Inside you'll find two pieces of metal sticking up where the antenna rubs against them. They may have worked loose....wider and not touching the antenna. With your fingers, gently squeeze these together. Rebuild phone in reverse order being careful to not overtighten the screws. If this doesn't work and you know your near a cell tower then I don't know. I've had it work twice for me and 1 time it didn't.