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I have just got a car with built in gms telephone. this requires a sim card in the car to work it.o2 do not do duplicate sims(or wont). another way is having a second sim card, with another number and diverting calls. this is however expensive.this is a business line so i cannot change networks. helpdave

Without changing network i do not know a way of doing this. however to be perfectly honest personally i would opt for a good in car bluetooth kit professionally installed and use that with your existing handset.