At the weekend, my friend tested at 24Mbit/s and was watching Sky Go coverage of the Grand Prix, tethered to an iPad. They are on UK Vodafone contracts.
However, during the storms, the Vodafone data network repeatedly failed or they got 'No Service' at all. Although there phones were on roaming, they did not switch over to Movistar.
I have ibred and UK O2 phones and both were fine.