Bonehead

I'm thinking about a new mobile phone but as I never take much notice of the ads and what's currently available I'm after a few suggestions.

I want to stick with PAYG as I mainly use the thing for texts and short calls.
I'm not bothered about anything with games but I wouldn't mind something with a camera and the ability to record calltones (A mate recorded a girl with torrets -spelling- have an attack and use's it for his calltone. It's worth phoning him when you're stood right next to him to listen to it. V funny)

It would be nice not to have to change my number - isn't that an option with some companies?
I'm with o2 at the moment and there coverage is s***e so I'd like someone a generally bit better signal (Im in the east midlands)

As far as PAYG prices are concerned aren't T-Mobile generally the cheapest?
If so, where's/who's got the best prices.

Tony