Why does my phone say no service and iMessage not working?

This is most likely an issue with your carrier (Sprint) You need to go into your local Apple Store, if you don't have one near you, go into a Sprint Store. You pay too much for service to be left with an non-working phone.

You can try:

Perform a "hard reset" on the device by pressing down and holding the home button and the sleep/wake button for up to 30secs. until you see a black screen with the Apple logo, then release.

Then test to see if it solved the problem.

Ever since yesterday my phone has said No Service where the bars and 3G used to be, but I can still send and recieve messages and calls.

Then you have service but you also have some other problems. Standard troubleshooting...

1. Try a Restart by pressing the sleep/lock button until you see the slider. Slide to power off. Restart by pressing the sleep/lock button until you see the Apple logo.

2. Try a Reset by pressing the home and sleep buttons until you see the Apple logo, ignoring the slider if, it comes up. Takes about 5-15 secs of button holding and you won't lose any data or settings.

3. Remove all apps from Recently Used list...

- From any Home Screen, double tap the home button to bring up the Recents List

- Tap and hold any icon in this list until they wiggle

- Press the red ➖ to delete all apps from this list.

- Press the home button twice when done.

4. If still a problem restore with your backup.

5. If still a problem restore as new, i.e. without your backup. See how it runs with nothing synced to it.

6. If still a problem, it's likely a hardware issue.