Can I take the SIM card out of my Samsung and put it in a iphone 3G?

The Samsung is a TracFone & the iphone is no longer being used but it was purchased at the AT&T store.

IPhones don't have SIM cards so no

Depends. If the samsung is a 4g phone, the you will have to call at&t to have them make the sim card usable in the iPhone. Reason for this is that the iPhone 3g does not support 4g

Yes you can take the sim card out of the Tracfone and put it into the Iphone 3G. But you can't get service for the Iphone using a Tracfone sim card.

Tracfone locks their sim cards to the phones that they are activated with. You can't use the sim card in another device.

Tracfone sim cards only stay activate for 30 days after the service was shut off. Either buy using all of your Tracfone minutes or by not adding another airtime card before your service end date, your Tracfone sim card will become useless. After 30 days if you want to add more airtime to a Tracfone with a sim card you will need to contact Tracfone and get a new sim card.