Originally Posted by DEVIS
What you're talking about is called SIM Cloning and it is highly illegal. It can be done, with certain underground equipment, but if the operator gets wind of this, they are in full legal right to terminate your service as well as charge you their early termination fee.
Tek this from a guy who uses 2-3 different phones a week. It isn't a PITA or RPITA or MRPITA or whatever acronym you want to give it. Besides, if you're running through an airport to catch your plane, which mind you is a place where you can't use your cell, switching the SIM from one phone to the next should be the last thing in your mind. Besides, I cannot comprehend why would one want to do this unless a phone to you is like a purse to a woman. I am like that and I've learned to live with that.
Last thing... FYI... you need a blank SIM, a SIM card writer and software.
And only ONE PHONE must be on. You cannot have both on at the same time.
Ok I'm done
Cloning the IMEI (International Mobile Equipment Identity) number is Higly Illegal in the UK (at least) and people caught doing it are dealt with severely.
Back in the early days of GSM in the UK, I knew someone who had his work mobile number divert all his incoming calls to his personal mobile and then only made out-going calls on his work mobile during the day and reversed this at night (I think). This was (if I remember correctly) to take advantage of the rates/free minutes that he had on each phone at different times of day.