Malcolm,
my own experience is that 3G isn't reliable here yet. It's still not that good in central London so there's doubts as to whether it will make it before 4G overtakes it. For backup you will have to stick with 2.5G on the GSM networks.

On a related point, I'm having great success using VOIP here on my mobile. I have a lot of telephone traffic with the UK and Europe and it was costing me a fortune. Now that I have my Nokia mobile set up I can receive calls made to my English phone number, free to me and only UK rates to the caller. I can make calls for free or very little. You need to be in WiFi coverage so it works at home and I'm progressively adding the bars and restaurants I frequent. It works very well over the 1MB Iberbanda as long as I'm not downloading a movie at the same time! It's cheaper to call Spanish numbers than my Movistar mobile. Interestingly, I phoned Movistar to cancel the contract and, to keep me, they have given me 6 months free of the minimum charge. I'm just keeping it now to have a Spanish number.

Pete.