I've had my (gay) iPhone 3GS for well over 3 years now. It does what I need it to do, and it does it better than any other phone, with the exception of newer/faster iPhones.
Its robust - although I have had to order yet another new case where its lost an argument with a desk partition, and it does not sport a crack in the iPhones case, and a chunk out of the screen
- functional, reliable and easy to use.
As things stand right now, if I had to replace it, it would be a gayPhone 5, as the 4S is too expensive for older technology. Android is the only viable alternative (RIM are dead, and MS are not getting the traction), but there is no usable email/PIM available for that platform without giving an Ad company full rights to your world.
I tend to buy my smartphones outright, and use a very cheap (free
) tariff which is 250mins/unlimit text/1Gb data on the O2 network. I don't really use it too much for work, as work provide me with a Vodafone SIM, which is pretty useless around these parts, so its on permement divert, and left in the drawer