The 310xt is the bomb. The best £300 (or less) GPS watch that you can buy.
I've owned a Garmin 110, 205, 305, 310 and now a 910.
I've used a
Nike Sportwatch, MotoActv, A range of Timex and Polar efforts and Garmin wins out across the board.
Only downsides are the truly awful software.
With that said, if it's just a case of replacing the phone, you could spend £100 on a 305 and it would do just as good a job on the bike and running. Only lean towards the 305 if you've an eye on swimming with it, or you've got money to burn.