You do not need a phone number to use iMessage. I don't have an iPhone and I message all the time using my Apple ID email address, and I have additional email addresses associated with my ID so that I can use Messages and Facetime on my iPad, iPod Touch and my Mac.
You have provided no details at all so Without knowing what you have tried or exactly what you are experiencing, you can start here for help.
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
iOS: FaceTime is 'Unable to verify email because it is in use'
Using FaceTime and iMessage behind a firewall
iOS: About Messages
Set up iMessage
iOS 6 and OS X Mountain Lion: Link your phone number and Apple ID for use with FaceTime and iMessage
How to Set Up & Use iMessage on iPhone, iPad, & iPod touch with iOS
Troubleshooting iMessage Issues: Some Useful Tips You Should Try
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
FaceTime, Game Center, Messages: Troubleshooting sign in issues
Unable to use FaceTime and iMessage with my apple ID
How to Block Someone on FaceTime
My Facetime Doesn't Ring
Send an iMessage as a Text Message Instead with a Quick Tap & Hold
To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
How to Send SMS from iPad
You can check the status of the FaceTime/iMessage servers at this link.
Thanks you all!
Well, my ID is accept, but when I put the mobile number of a friend an exclamation mark appear. It says that the number is not register in iMessage. So I think my problem is how to register my contacts!
No - your friend has to setup and register messages on his device before you can reach him. You can not register for him. He has not set up messages on his device yet.
Messages only works with other iOS devices and Macs running Mountain Lion. You cannot text an Android phone or any standard cell phone either.
Also, the button "send" doesn't allowed me to click on it.
Check Settings>Messages>Show Subject Field>Off. Make sure that is set to off.