Ah, thanks for the clarification. Very daunting but at least I know it's theoretically possible. If only this was more practical!
It appears that you'd have to have the phone taken apart just to use the foreign sim card, which is impractical. Maybe it could be stuffed below or above the battery, of course assuming the little wires could fit through some crevice or crack somewhere in the back. Otherwise, this type of hack basically just makes it possible to find your favorite foreign sim card, stick it in and close the device back up.
When I traveled around Germany and the UK this summer, it was super convenient to just switch to the new sim when I needed but I don't see that this will be possible even with this type of hack. Damn!