We use these below on on work vehicles, they work very well, give realtime tracking as well as 30 days history, you need a sim the same as all the rest, it works out about £3 per month in data costs on a normal Voda monthly tariff.
Make sure you wire it to a permanent live as these dont have a internal battery.
http://www.ebay.co.uk/itm/2907035960...84.m1423.l2649