Why can my Samsung i900 only receive short messages but not send them?

If the mobile phone can't send short messages, I suggest you check whether you can answer the phone. If not, please check whether the machine signal is stable and whether the phone bill is sufficient. If the phone normally receives calls, but can't send short messages, suggestions: 1. Check whether the information center number is correct (please contact the local network operator for the information center number, and the telecom card has no information center number setting) 2. Try to replace another SIM card. 3. Check whether the machine has a firmware/system update push notification. If yes, please upgrade your phone to the latest version. 4. If it is invalid, please back up data (contacts, multimedia files, etc.). ) and restore the machine to factory settings. If the problem still exists after the above operation, please take the purchase invoice, maintenance card and machine to Samsung service center for inspection.