Hi Stacey,
Firstly, have a moozy on over at this comparison site
http://www.latestmobiledeals4u.co.uk/and see which one is right for you. Be wary of the cashback deals though, some people have reported companies taking agessss to send cheques etc - but its not to say they're all like that.
Since a couple months ago - I can't recommend O2 for the 'included' in your minutes access to '08' numbers - they've changed policy and are now charging it outside of bundled minutes. So, for me, the deal where I get free calls (as part of my bundled mobile minutes and access via 0800 number to Swiftcall) will finish by the end of september.
Apart from that, and seeing you want text's over voice minutes I think you can filter the site above to show that.
Handset choice.. nip into WHSmith and pickup a copy or just read it if you dont wanna buy it! of What Mobile - i think theres a couple of other titles too, and read through their reviews of various handsets to help make up your mind. I'm a gadget guy and I had the Nokia N95 that everybody is raving on and on about, I took it out of the box, played with it for 2 days and thought it was crap - and returned it. It's fine for what it is, but it's not fine in terms of performance for what it is - ie whats the point of GPS if it's not real time? why have a 5 megapixel camera when it's performance is actually as good as a old 2.1 mp digi camera from a few years ago...
thats just me though - you may find it or something similar absolutley fantastic!
final tip, see if you can upgrade your current contract to include a special deal - mention to them on the phone you want to go to another provider and tarrif and you want PAC code and watch them transfer you to the 'retention' dept. and see what they offer and wangle them to throw in extra stuff for you to stay .. like 500 text for no extra monthly charge!
Cheers! DtM West London & Slough UK!