I did the online chat for this error message when trying to send a text after getting my phone just a few hours ago, and this is what the chat person told me to do, so the next person doesnt have to go through it.
Eliena R: Press Menu, then tap Settings.
Eliena R: In Settings, flick Up and tap System updates.
Eliena R: Tap Update profile.
Eliena R: You will see Device Configuration - The network is preparing your service. Please wait.
Eliena R: Do not interrupt this process.
Me: ok update complete
Eliena R: That's great.
Eliena R: Now , Tap OK to return to Home screen.
Eliena R: Please try to send message.
Texts work fine now. Thanks!