This is for our UK pilots with a Flytrex. Mine is a 2G unit but works well with 3/4G cards. I use a pay as you go sim card, but the top up is usually about £10 for 1GB with 30 day expiry, a typical month of flying uses hardly any of the data allowance. Today I spotted an EE data sim in Tesco for 99pence and 200MB free,30 days expiry,you are expected to top it up when it runs out,it works perfectly in the Flytrex,will probably last me 30 days, and then get a new one for 99p. You need to activate it on a phone or tablet,or in my case a MIFI unit,only takes a minute, and then you are good to fly. PS I love my flytrex,it is good to get home, and analyse your flight in great detail.