Hi... apologies if this has been posted before, hopefully this isn't a dumb question. I currently have a RAZR with AT&T. If I buy an iphone it comes with it's own SIM card. Since I already have an AT&T account and a phone with a SIM card, what happens when I activate the iphone? Does it de-activate my old SIM card? Or, when I receive a phone call, will both phones ring? Will I be able to use the RAZR or the iPhone (i hate my phone right now but it would be nice to use it if I was going someplace where i wouldnt' want to take the iphone, like the pool). Thanks for any info!