Can i use my old straight talk sim card on my iphone?

I'm going to get an iphone. Now i keep seeing people say they buy a micro sim from straight talk and put it in their iphones. I already have a straight talk phone, so can i just take my old sim and use that?

No you have to get a micro sim card from straight talk.

No. You have to buy a sim card from the Striaght Talk website for $15. Tracfone/Net10/Straight Talk "lock" their sim cards to the phones that they are activated with.