iMessage is quickly becoming a standard in communication, but it needs to be setup correctly to work. Here’s a quick check to make sure it’s setup right in iOS 5
1 Go to your Settings
2 Touch Messages
3 Make sure iMessage is on.
4 Now you can select your receive at address, on your iPhone this should already contain your phone number, but you should also add your Apple ID. Touch Receive At and sign in to your Apple ID.
iPads and iPods are slightly different only because they don’t have the mobile number.
You will see a sign in to Apple ID only, sign in or create an account for free.
Extras:
If you use the same Apple ID on two machines, messages will be in sync. If you prefer to have separate messages, then you create and login with two Apple IDs.
If you want to make sure you only use iMessage and not your carriers SMS (text) message service to save money, turn OFF Send as SMS from from the first screen. But keep in mind, you will only be able to message Apple devices.
You will know messages are iMessages when they are blue, SMS is green.