Hello Myron Holmgren,
Welcome to Microsoft Community.
Normally, the Surface Duo 2 works with all the major carriers in the U.S., and it should work with AT&T, T-Mobile, and Verizon Wireless networks.
However, if the problem is that no SIM card is correctly recognized on your Surface Duo 2, you may need to send your Surface Duo 2 device to the Surface after-sales support team to have your Surface Duo 2 checked out:
How to get service or repair for Surface - Microsoft Support
I wish you all the best.
Best Regards,
Mitchell | Microsoft Community Support Specialist