A cellular telephone (102) in a vehicle includes a data carrier system comprising a first semi-permanent Subscriber Identity Module (SIM) (200) selectively couplable to the cellular telephone (102) and a second SIM (300) selectively couplable to the cellular telephone (102) in preference to the first SIM (200), the first SIM (200) being arranged to be decoupled from the cellular telephone (102) when the second SIM (300) is coupled to the cellular telephone (102). During a predetermined period of time, the cellular telephone (102) is arranged to be ensured of a supply of power and the second SIM (300) is arranged to be decoupled from the cellular telephone (102), thereby causing the first SIM (200) to be coupled to the cellular telephone (102) for the execution of a task requiring the first SIM (200).