I took the plunge and put three strips of tape over the back of the sim card, cut it to shape, and have had no problems this week, amazing!
Still, if mine has any more problems I'll have to just go on at HTC and get them to fix it but for now, this is the longest my phone has gone without restarting it in over 2 months!
Oh, I did try HTC support once more but didn't even get a response, that's four times I've put in a support call since January that they've ignored. Shall be moving to Nokia for my next phone I think.