If you’ve updated your iPhone to the latest iOS 7 that came out last week, you might notice a lag when using the new keyboard in the apps that support them (such as the built-in messaging app).
Luckily, there seems to be an easy workaround fix.
– Go to Settings > iCloud > Documents and Data
– Toggle the setting to Off
– Go back into the Messaging app and test the keyboard
– If it works okay, you can turn Documents and Data back on
WARNING: It has been reported if you go into iCloud and Storage & Backup the problem might reoccur.
Another option is to go to General > Reset > Reset All Settings. This will only reset the settings and it won’t delete any data or media that you have stored on your device, but you’ll have to go back into the Settings app and change everything back to how you had them before.