Worked for me, on iPhone 4. It is easier if you have a micro-sim to place over your mini-sim to trace around as a template.
I tried it, as gazzeg said, he/she is correct. The first sim portrayed above (blue) is the old sim with the large golden part. I have that kind of sim. I cropped it down to perfect size with a lot of sandpapering and it fits perfectly into the slot. BUt it still doesn't work.
I suggest that you take a MICROSIM and compare it to the old sim you have, if the golden contacts are the same size then you are good to go but if the old sim has larger golden contacts then don't do this as it won't work.