My iPhone 5 won't let me text another iPhone user?

I've got an iPhone 5 and I want to text another iPhone user, but it won't let me. When I want to text them it will only let me iMessage them.

Isn't that the same? And buy a Galaxy S3; much better

If the phone is new it probably just needs the settings changed to allow you to use certain features. Phone your provider and they will do this while you are talking to them. Only takes a few minutes

Thank you Galaxy S3 user. NO Help

Galaxy S3 user. I prefer quality