On the face of it, Vodafone's iPhone plans don't look particularly cheap and doesn't offer any free Wi-Fi hotspots, but it turns out that there's a catch you may be able to use to get a lot more data. Futurist Mark Pesce, an existing Vodafone customer, realised that his current cap plan could be spent on data as well as voice and text. While this isn't mentioned anywhere in Vodafone's explanations of its iPhone plans on its site, Pesce asked for the full printed terms and conditions in store, and it turns out that this also applies to the iPhone: you can spend your cap on data for 12 cents a megabyte (with a 50 cent minimum each time).
So if you're not planning on making heaps of calls, you can spend your cap value on data instead, and potentially get several gigabytes without spending anything extra. If you want to do this, insist on seeing the printed terms and conditions in store and get them acknowledged by the salesperson, to save any possible billing arguments later. If you try this at a Vodafone store, let us know how it works for you in the comments. (Thanks Mark!)