My text messaging worked before, but isn't working now:
Check your Balance - If you are not on an unlimited plan, you may just need to add money to your account.
Clean Out Your Message Folders- The messages you send and receive are stored on your phone. Each device has a memory capacity, and extra stored messages can get in the way of sending an receiving. Clean out Inbox/Sent, Outbox/Received, and Drafts/Saved folders.
My text messaging has never worked!
Check the number you are texting- Use the area code (10 digit) dialing to ensure that the message will be sent.
Check your balance to make sure you have sufficient balance to text message.
If you just activated your phone, turn it off for 30 seconds and then turn it back on. Attempt another text message.