I have the Samsung Brightside and I have noticed that some of my text messages have been deleted. Sometimes it is just the sent messages and it happens with multiple senders. Is this because my phone is low on text message memory or is it some other problem?
Some phones do automatically delete the oldest messages if the inbox or sent box gets full. I've heard (though not experienced it, I try to keep my messages folder pretty cleaned out) that it seems to be random at times, which messages get deleted. I have received a warning that the inbox is full - and then go in and clear messages to free more space for incoming.
Lock the messages you absolutely need to keep, and then erase all from sent, drafts, and inbox regularly. Also, rebooting the phone after you have cleared the messages will help the phone to better "see" the now cleared memory space.