Mine is not automatic, I have three sim cards. One I keep in my Mercedes, one in me porsche, and ofcourse one in my handset. What happens is, I can set the master SIM by using a sim command (*123#) - All of the sims if on can make calls and send SMS but can not receive calls. Only the master will ring. If I am in my Mercedes, I give this command and it works - if in the porsche, the PCM thinks I am dialing a phone number (The merc has a phone with a cradle, the porsche has PCM only) ... so its kinda pointless to have to accept calls on my handset and can dial out of the car ... I called my teleco and they were clueless, porsche dealership - just as clueless