Others make the point about calling costs, but if you want data only (say for a tablet/laptop/mifi) an any-network roaming SIM would be very attractive. For exa

Others make the point about calling costs, but if you want data only (say for a tablet/laptop/mifi) an any-network roaming SIM would be very attractive. For example my current network is great in London, but has no signal at all in my hometown. It would also be handy for use on the train, where coverage on all networks is patchy.