GPRS - General Packet Radio Service With GPRS the  tracker is connected all the time and positions are sent at pre-set intervals. Each position is aprox  36 bytes only, but a 'header' must be also sent, which doubles the size of data being transmitted. Even though some operators charge for the header, the size of data sent is still very small. The internal algorithm makes sure that data is sent only when your vehicle moves by a set distance, time and angle keeping costs very reasonable - with default settings travelling 1,000 miles per month you can expect to transmit approximately 1MB of data. Cost per MB varies from operator to operator, On orange it cost aprox £4 per MB on PAYG cards. If you are using a PAYG SIM card, you will need to make sure that it is charged, otherwise the unit will not be able to transmit. It will, however, store positions in the internal memory  and will transmit them as soon as you add credit.