For all those new iphone 4 users they would like to use their old mini sim card, as iphone 4 needs micro sim card so they need to cut the normal sim card to convert it into a micro sim card which can be inserted in iphone 4
Here is how to video on how to cut your mini sim card and convert to micro sim
[ame="http://www.youtube.com/watch?v=ZUpkX4P6FWA"]http://www.youtube.com/watch?v=ZUpkX4P6FWA[/ame]
Still after watching the above video if you are unclear about how to do it then you can also refer these how with step by step procedure
here and
here