put iPhone 4 SIM card in iPhone 3gs ???

Hi folks,

I'm a doctor. I use my iPhone instead of a medical beeper, always on, always need to be available to others.

I upgraded to iPhone 4 from my iPhone 3gs. iPhone 4 is fine. I am keeping my 3gs at home as a backup, just in case something happens to the iPhone 4 like it gets wet or I drop it or something.

In the past, I could always pop the SIM card out of the 3gs and put it into any other spare cellphone at home as a backup and that would work because all phones take regular SIM cards. But this iPhone 4 has a micro-SIM card. Can I take the micro-SIM out and somehow put that in the 3gs if I needed to use my backup phone in a pinch? Is there an adapter or tray which would make it work?

Thanks in advance,

-- Josh