My phone has had working 4G for months, now suddenly it does not connect. 3G is fine. It has additionally become laggy and slow in the last week. I don't know if the two problems are related. 4G will turn on then off over and over until my phone is hot and the battery is flat. Sometimes it detects the Sprint network and then turns off, but most of the time it doesn't even get that far before turning off again. Any ideas why it is doing this? I have installed some new apps since then, but have not updated the system software.
What model phone do you have? Have you tried power cycling the device to see if that helps at all? I would like to check your area if you would provide a ZIP code. If you are in a pre-launch 4G LTE market there may be some work still being done on the towers. I can check and see what the story is. Beyond that I would be happy to troubleshoot further if that doesn't solve the concern.