The final solution (I hope):
I went to the Apple Store and got a replacement iPhone4.
Reasoning - they reported it as a speaker failure.
I explained this forum and other people with the same issue, and my sceptisism that this is anything but a s/w fault. The issue, they beleive, is a hardware problem gradually getting worse and reacting badly to s/w updates, not just IOS 7.... (don't shoot the messenger please).. then getting to a critical point where it was unrecoverable.
They told me they could replace the speaker, but that wouldn't resolve the 2nd issue I have - losing the network and having to do a full reset - which I've been having for 6 months (now daily).
I did get a very good discount from the usual hardware swap-out price offered... I'm on my 4th iPhone 4, due to various problems....I made a strong case for not paying anything, but that wasn't going to happen, I was told.
I have made a log of the issues, and if things go wrong on this new phone, I'll add to it.
I've spent FAR too much time trying to sort this phone out. I feel like I'm a DOS PC user running a shoddy game sometimes. So I'm really looking forward to just using my phone to make calls, and actually getting my work done. Yay.