Can i use a regualr sized sim card for an iphone 4?

I want to by an iphone an I have a regular sim card can I use it for an iphone

No - it uses a micro sim. Your network will swap your existing one for a micro if you call into their store or the full size one can be cut down

No.microSIM required.

I had a regular sized one and I just cut it to match a micro sim size