I’m still very happy with my 3GS*, but it’s really quite old for a phone and the battery life was never great to start with. As a device it ace and I won’t be without a smart phone, but they aren’t for everyone – friend had a 4, didn’t use the functions enough to make it worthwhile, so sold it and went back to a std phone.
Pure and simply I’d be equating the cost of the phone and say a £10 a month giffgaff contract against what you can buy the like of a Galaxy S2 (or such like), and bearing in mind they will be faster phones.
Though it maybe you don’t need the latest all singing and dancing options, so maybe a cheap apple will be just the job, as they are quite brilliant and ‘just doing the job’.
* I will mention the fact that my own 3GS is rubbish as a phone where we live, but no one else complains of these problem so it must be just me…