Can i use my 4g sim card out of a focus flash in a iphone 3gs?

I have a AT&T samsung focus flash which broke. My buddy gave me his old iPhone 3Gs and i was wondering it will work or is there a way i can make my 4g sim card work in the iphone. Any help is greatly appreciated

Assuming the 3GS is also an AT&T phone, then you would be able to stick it in & it will work fine as is. Of course don't expect 4G speeds from a 3G iPhone.