I recently got a Samsung Galaxy S3, it came with a 4g LTE sim card in it. This is the first phone I've ever owned with U.S. Cellular that has a sim card. Would it be possible to plug this into an unlocked Iphone 5?
I haven't tested it out but I think it could. Verizon iPhone 5s use CDMA and LTE as well. I'm not sure if US cellular has nano SIM cards, but there are plenty of instructional sites on the Internet showing how to cut a bigger one down to size. I think it should work in Verizon's iPhone. You should give it a try.
The Verizon iPhone 5 will probably not work. Even though both use CDMA, verizon locks the cdma bands on their phone, while unlocking all the gsm bands.
None of the CDMA networks will allow you to take out the LTE SIM card and use it for an unlocked device. Not Verizon, US Cellular, Sprint none of them.