When you registered mobile9 would have sent an email to your email inbox. Please follow the instructions in this email to validate your account. Check your junk mail if it's not in your inbox. You can resend it by looking at the top of this page. There is a "resend validation email" link.
If you typed in the wrong email address when you registered you can change it at:
If the above fails please post here and an admin will send you a message to the email that is associated with your account with instructions on how to validate it.