I keep trying to text message friends from my contact list but I keep getting the error message that I am testing an invalid number and to use a 10 digit number. I've checked all my contacts and all of them are 10 digit numbers.
The worse part is I can get text messages from them but I can not initiate messages to them.
Have you reset your network settings? Are you trying to send sms or mms? Double check the settings for messaging. Double check the numbers to make sure they are correct. Reset the phone by holding the power and home buttons until the apple logo appears.