I remember somebody here saying the cheapest way to get mobile data is to buy prepay microsims from eBay. Is this a good idea? Do I just buy a new microsim each time? Don't the phone companies get wise to this? I don't intend to use a lot of mobile data because we get BT OpenZone as part of our landline deal and wifi is free at places like McDonalds and Wetherspoons pubs.