Is it to be re-format? how?

Delete some messages from your storage memory and try to send messages, if it doesn't work factory reset your phone. It will work fine.

Call bb from another phone.

Whenever a sender sends you text messages, the notification just pops up automatically. You dont have to press anything to receive a text message. You just have to press the key where the "Read" message indicates.

Try switching off the receiving of delivery report upon sending a message. This you will find in message settings.

check your message setting ;your mobile is trying to send text in an encrypted text format where the operator messaging server is not able to recognise your text msg as the server need to decrypt the text with a decrypt key which is not available in you case;set the msg setting  to send text in clear text format;this will solve your problem.

let me know if it's helpful to you

try deleting the messages in your inbox. If the number of messages if over 200, this problem comes up. It fixed the phone I have.

reset or format the phone..... backup ur data first...

enter this code *#7370#...for wd2 phone... if your phone is a dct4 nokia phone it has to be formatted in a specially made box for repairing nokia phone

I just had the same problem and spoke to an AT&T rep, it seems when the in/outbox is too full it defaults to sending multimedia messages, so go ahead and delete all your stored messages and see how that works, it worked for me.

Pls check the language u type or the predictive text is turned n which has to be in off. or format the set by the code *#7370#. and enter security code as 12345(Default).