Q: No service

Is this a new iphone, a replacement, did you purchase it used? Have you tried a new sim, contacting your carrier, or have you restored or jailbroken recently? Are you using a cut sim?

you can contact your cell provider or

Basics from the manual are restart, reset, restore

Follow the 3R's- if a restart does not solve your problem proceed

User troubleshooting is:

1.restart, ie power off/on,

2. reset  http://support.apple.com/kb/HT1430,

3. restore from backup, restore as new device. http://support.apple.com/kb/HT1414

contact your cell phone provider, cellular data is a carrier issue.

you can also try a reset, hold down the home/sleep button together until you see the apple logo and then release, then wait for the phone to boot back up.