Both Mrs C and I have HTC Desire phones, have had for nearly a year now and have been very happy with them.

Yesterday, Mrs C's phone came up with some kind of message (she didn't read/understand it) which seemed to result in the phone rebooting - thereafter, all her SMS have disappeared (and she had loads in there).

Can anyone suggest what has happened, and are the messages retrievable?

It's a bug I'm afraid. Not sure if its HTC or Android. Lost all mine q few weeks back. Have not heard a way to get them back. Some have said delete HTC sense sync but didn't work for me. Now use sms backup.

Not come across this issue. Without knowing what message came up before the phone rebooted, its going to be difficult to ascertain what the problem is.

Although a bit late now, but can be helpful to you, backup up your text messages. SMS Backup & restore
is a great app, that is simple to use. It allows scheduled backups, that will automatically backup your text messages.

Not as bad as the android bug which would send texts to the wrong numbers

I have read about malware text messages that functioned like this. Restarted the phone on reading and then did naughty things.

Thanks for the advice - I don't think that there was anything life or death on there, more just stuff that she wanted to keep for semi-sentimental reasons.

Think she has got used to the idea that they are gone now.