Can we use the new Micro sim from iPhone 4 also in the iPhone 3GS and iPad 3G?

[OceanView]

I have the iPhone 3GS, iPad 3G, iPhone 4 (in transit) and a micro sim adapter.
I would like to use the new micro sim from the iPhone 4 to use on one of these three devices at a time as I choose. Is this possible?

I'm aware of the changes to the iPad APN that needs to be made.
Also, if the new micro sim will not allow me to do it, can I just cut my exising sim from my 3GS and use on the iPhone 4 instead?

Main concern is AT&T detecting and either charging me additionally or disabling data plan on my account.

 

[X-rated]

I went to AT&T today to get a new sim card because AT&T screwed mine upon activation. I asked the AT&T guy about it and said they are the same and he put my new sim card in from the same stack as the Ipad sim cards