Check the cell signal
icon in the status bar at the top of the screen. If there are no bars, or if it says “No service,” try moving to a different location. If you’re indoors, try going outdoors or moving closer to a window.
Check to make sure you’re in an area with network coverage. Go to your carrier’s website to see network coverage areas.
If the cellular network isn’t available, connect to a Wi-Fi network if possible.
Make sure airplane mode isn’t on. From the Home screen choose Settings, then turn airplane mode off. If that doesn’t work, turn airplane mode on, wait 15 seconds, then turn airplane mode off again.
Make sure to include an area code for every phone number in your contacts list that you use to send or receive text messages.
Turn iPhone off and back on again. Press and hold the Sleep/Wake button on top of iPhone for a few seconds until a red slider appears, then drag the slider. Then press and hold the Sleep/Wake button until the Apple logo appears. Tap Unlock and enter your SIM’s PIN if the SIM is locked.
IMPORTANT: If you enter the PIN incorrectly three times, you may need to enter a Personal Unlocking Key (PUK) to enable your SIM card again. Refer to the SIM card documentation or contact your carrier.
There may be a problem with your wireless service. Call your carrier or go to your carrier’s website.
If you’re traveling abroad, you may not have Internet access because Data Roaming is turned off (the default). Turn Data Roaming on or connect to a Wi-Fi network. To turn Data Roaming on, in Settings choose General > Network and tap Data Roaming. Data roaming charges may apply.
IMPORTANT: Data roaming charges may apply. To avoid data roaming charges, turn Data Roaming off.
Restore the iPhone software. See Updating and Restoring iPhone Software.