Since iphone 4 need micro size simcard, lots of iphone 4 users need to convert their simcard into micro size in order to use their old number without buying new number. So what I found were :
1. Convert using "micro simcard cutter" where usually u can get this from ebay with lower price. but it might takes longer time to deliver to your country/location. but if you buy them, you will be provided few simcard trail where u can reconvert your micro simcard into origional size.
2. For people in rush, you can download and print this pdf, and cut your simcard manually using scissors or sharp knife. but make sure u dont cut the chip (yellow).
Download here : http://www.thechinacellphone.com/micro_sim_template.pdf
and if u unsure what to do, just watch the tutorial here :
if this link doesnt works, just type in goggle "convert sim to micro sim pdf" and you will find it.
that's all. hope it works for everyone!