I seem to have found that of late, maybe since the upgrades, the messaging seems to readily'drop out' (keyboard disappears) and freeze when using my mobile phone. It's probably linked to varying signal, but it seemed to be much more tolerating in the past and you could keep typing a message and send when the signal was more stable.
Also, perhaps it linked to the intermittent thing, the 'Delete message' check box is not ideally placed being so close to 'Send' and when the message function freezes, when it resumes it can accidentally select the delete option and you risk losing a conversation string if you can't cancel at the confirmation screen that follows!
Hope I'm not sounding too petty and it's better to live with the issues than have no forum!