SMS and MMS stopped working on AT&T 640 with AT&T service


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Aug 8, 2014
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My brother's Lumia 640 stopped being able to send and receive both SMS and MMS on Sunday. The last message he received was Sunday morning until he had me look at his phone Monday night. Neither the AT&T APN settings nor the messaging service number had been changed.

The phone didn't give an error if he tried to send SMS, but the messages were never delivered. If he tried to send MMS, either with a media attachment or a group text, it would pop up an error message that said the message could not be sent. After trying everything I could think of to troubleshoot, including using my working SIM card in his phone, we determined that it was something with the phone itself.

We did a backup of his phone and then performed a master reset. We restored from the backup, and after updating the messaging app both types of messaging started working again. I'm just curious if anyone else has experienced this before or might know why only a master reset would resolve this sudden issue. All the messages sent to him while the messaging was not working were apparently lost. Once we got messaging working again, he was only receiving new messages. He never received the others.

Edit: His Lumia 640 is running the latest public release of Windows 10 (build 14393.693).

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