USBFever could save you a lot of hot-swapping -- assuming at least one of those SIM cards is currently in an iPhone 3G or 3GS. It looks like an ordinary, bulky external battery, but inside packs room for a second SIM. Swapping is handled via an on-phone application and, according to the online instructions, it'll take about two minutes for your handset to figure out exactly what the heck is going on and reconnect to the different network. Sadly the phone can't monitor both cards simultaneously, so if you frequently receive calls on both you're stuck with that second device, but if by day you're a mild-mannered corporate user and by night you switch over to your secret personal account, this could be for you. $60 gets you in to the card-swapping party -- just leave your keys in the bowl on the way in.