PocketMatrix

I have two cellphones, both GSM-enabled. While I only really want to use one of the two phones at a time, I do want to be able to switch between the two phones that I'm using. (One of them is quite large, but the other doesn't have enough memory to view normal html pages.)

I've seen devices to backup and copy contacts off of SIM cards, but I'm wondering if there's such a device to
"clone" the whole sim card so I wouldn't have to go through the cumbersome business of switching the SIM card between them. (A few time I've taken the wrong phone with me by accident only to discover that I have a phone with no Sim card.)

Anybody know of such a device? Since I only really want to use it once, I'd hope it wouldn't be very expensive...