It's a 2-in-1 SIM card!
When Apple announced the iPad, the company surprised people by revealing that the device would take a special type of SIM card called a micro-SIM. Though the iPad has been on sale for a while, the whole micro-SIM thing hasn't really been talked about too much because the 3G version of the device had yet to arrive prior to today.
However, while it hasn't been a big topic of conversation, there were a few details about micro-SIMs uncovered in the days after the iPad announcement. Engadget's Chris Ziegler said back in February that if you wanted to, you could probably just cut a regular SIM card down to size. In other words, if you were really desperate to get an iPad running on a network that wasn't offering the smaller SIM cards and were willing to put in some effort, you could make your own micro-SIM.
Today Boy Genius Report confirms Ziegler's theory with pictures of AT&T's new micro-SIM cards. The carrier just got these in in time for the launch of the iPad 3G and as you can see, they can actually be used as a regular SIM card too.