I may have mentioned this before, but every time I travel abroad I find that the usefulness of my iPhone is dramatically reduced by the lack of a reasonably priced data tariff. How much would be reasonable? I think about £0.10 per Mb would be about right; low enough that email and casual web use can continue unimpeded but high enough to deter video streaming and music downloads (although I'm not sure why such a deterrent might be desirable).
 
Why is this important? Unlike most people, I primarily use my phone for Internet access and email, so I am particularly affected by a lack of data access. I could just pay the £3 per Mb they charge but I'm too tight, so I suffer instead and hope for change. Unfortunately, hope sends very few emails.