Iphone, is a sim card all i need for 3g?

i recently got a iPhone 4 and it doesn't have 3g i know i need a sim for 3g but is it only a sim card i need or do i need actual cell phone service which i have no intent to get.

Anonymous2013-09-22T01:50:37Z

You need a cell Phone service in order to get 3G data.