What's the best data plan when you're not sure how much you'll be using it each month? Three and Vodafone are offering plans at £7.50 and £10 a month, respectively, but I don't fancy being stuck in a contract. Saying that, there might be times when I could use the full month. Any thoughts? At this rate, I might just cut down a giffgaff sim, should the iPad stock ever arrive.