I can't find where to put the sim card?

I have the iphone 4 and I can't seem to find where to put the SIM card, I thought it should have that little hole on the side like the iPhone 4S but it doesn't

Look on the right side of the phone. There should be a little tray.push a paper clip into the tiny hole and the sim card tray should pop out. If your iphone does not have that tray, then you may have a knock off.

If it is a Verizon or Sprint model, it is a CDMA only phone and doesn't use a SIM.