I have one of the above mobiles, purchased in August, but when i have been on a lengthy conversation the phone switches itself off ! At first I thought it was my cheek pressing on the OFF key but this is not the case, I end up turning the phone back on and having to phone the person back again, and once in conversation you can guarantee that it will switch itself off again. ANy ideas why its doing this, it never used to.
are you sure the battery didnt wear out? i know you probably checked, either that or try a new mobile phone battery in it, and see what happens. sorry, this has never happende to me though, im just guessing.
I had a similar problem a few years ago with a Nokia, it turned out to be a dry solder joint on the circuit board, as the phone warmed in my hands, (or with use) the joint would separate through heat expansion, and the phone turned off.