Can you put a metro sim card in a iphone 3g whitout unlocking it?

Can you put a metro sim card in a iphone 3g whitout unlocking it?

No, only straight talk sims will work

You can't use CDMA network to an unlocked GSM mobile.So, you will not be able to use your iPhone 3G with Metro (Metro PCS) network. To which network is your mobile locked with?
To get your mobile unlocked you can contact your network provider or approach third party unlocking services. I suggest remote unlocking service is a simple and easy way to unlock your iPhone 3G and to avail the service you can contact http://www.superunlockcodes.com/apple-iphone-3g/rs16wp9/ and use their free unlock instructions to remove the network lock easily.