Vodafone certainly used to provide matching SIMs for this purpose and maybe still do. I used the system in a company Pug 407 a few years back but the phone was also provided by the company so I don't know much about the ins and outs of it, other than I was given two SIMs.
You could dial out from either SIM at any time but only receive calls on one, switching between them by dialing *131#, if I remember rightly. Of course you seldom remembered to do this, so got your first call after setting off in the car on your normal mobile, then switched over to the car phone, then you arrived home and didn't get any calls all evening as they were trying to get through to the now switched off carphone and piling up on your voicemail.