iPhone 4 and switching back to the iPhone 3GS sim cards?

[Imola Ghost]

I'm not sure if anyone has thought about this but I don't see an easy way to do this. Since the new iPhone 4 uses a different SIM card than the iPhone 3GS/3G. How are users that are wanting to use another phone or iPhone for a while able to do this now?

 

[irich25]

microsim adapter