In Europe, it is common for cellular phone carriers to allow you to have two SIM cards for one phone number.  This way, you can have multiple phones to do different functions, but on the same phone number.  Or how about if you are traveling and just want a phone to make calls only?  Instead of moving your SIM card from one phone to another, just grab your phone only phone and away you go.   Its not an idea we really think about in the US. US cellular carriers don’t allow for this at all.  The closest we get to this kind of situation is if you have a Google Voice account and forward the number to different phones.

From an article on Mobility Minded on how this idea started:

How did that start? Many cars in Europe had an integrated car phone system as an option before Bluetooth car kits were on the market. It was a convenience to pop a second SIM card into the vehicle and be able to make and receive phone calls on the same number as the user’s mobile phone, without changing any phone numbers. But of course, there were some constraints:

1. The phone that was turned on first  – and registered to the network –  was able to receive and make calls;
2. If you turned on your car (the 2nd SIM card) without turning off your phone - the car phone could only make calls, while the mobile phone would still receive the incoming calls.

The easiest way to keep things straight was to make sure the first phone – the mobile phone was turned off before starting the car.

And now, we have Bluetooth car kits that can circumvent some of this.  But what if we could do more?  What if we had more flexibility?  What if we could convince the carriers to let us have more than one SIM card for our phone numbers?  Would this really be a help to us?

Mobility Minded has a poll up on their site to see what we think.  Maybe if enough people take it, it might make the cellular phone carriers notice?