Imessage can't be used

Method 1: Check the automatic setting options of date and time.

1. Enter "Settings" in the ios8 system.

2. Then, we click the "General" option.

3. Then click the "Date and Time" option and click Enter.

4. In the date and time settings, make sure that Automatic Settings is turned on.

5. Then open the iMessage option and click Open to activate again.

Method 2: Turn it off and then on.

1. The shutdown method is simple. We just need to hold down the power button of the iPhone by hand until the power-off slider appears.

2. Then slide the slider to turn it off, and then press the power button to restart the iPhone.

3. Finally, try to activate the iMessage service.