Sony Ericsson w830c reported the problem by SMS.

Are you a W830 user? Open the main menu-Information Function-Settings-SMS-Send Report, which can be turned on or off. In general, SMS reports are turned on. No matter who the user sends a message to, as long as the other party receives it, it will send you a message report. This should be no problem. If there are times, you may have sent too many messages at once. If there is any problem, take it to the maintenance center to brush the machine. Soon, this problem should be solved.