I can then use my iPhone 5 for any data I need when Im out and about (likely to be on the ground rather than in the air though) - Out of interest, for those that do use data in the air, how useful is it?
It depends how high you fly, and where you fly.
In my experience, the signal tends to be intermittent from as low as 1,500 feet. I've tried to get METARs and TAFs in the air using the internet, but had very limited success. It's probably easier just to ask ATC to get the weather for you.