Life saver! I dropped my iPhone 4s in water today. I really wanted to be able to use my number still, but have no other phone that takes a micro sim. I also couldn't even use my spare iPhone (3gs) because apparently my old sim card is too old for iPhones. So I was stuck using an old phone and an old number for the day.
On my first attempt at this the sim card kind of broke when I tried to cut into it. Luckily I had another dead sim that I could use, and it worked fine the second time. Now I can have my number and at least be able to use an iPhone.