Hello mgleboff,
Thanks for that info and choosing the Apple Support Communities. Based on what you stated, it seems you are experiencing issues with your iPhone showing No Service when putting a SIM card from a different carrier in your unlocked iPhone. To help with your situation, please follow these steps from this Apple resource on this issue:
Make sure that you're in an area with cellular network coverage. Then follow these steps:
- To turn cellular data on or off, go to Settings, then tap Cellular or Mobile Data. If you're using your iPad, you might see Settings > Cellular Data.
- If you're traveling internationally, make sure that your device is set up for data roaming. Go to Settings > Cellular > Cellular Data Options > Data Roaming.

Restart your device. If you're not sure how to do this, follow these steps.

To manually check for and install a carrier settings update:
- Make sure that your device is connected to a Wi-Fi or cellular network.
- Tap Settings > General > About. If an update is available, you'll see an option to update your carrier settings.
- To see the version of carrier settings on your device, tap Settings > General > About and look next to Carrier.
If you insert a new SIM card into your iPhone or iPad, you need to download the carrier settings for your new carrier.

If the SIM card is damaged, or doesn't fit in the SIM tray, contact your carrier. Learn more about removing your SIM card.

Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

Update your iPhone or iPad to the latest version of iOS.

Issues with your carrier or account might affect your service. Contact your carrier to:
- Verify that your account is active and in good standing.
- Make sure there are no outages in your area.
- Check that your device isn't blocked from receiving cellular services and is set up with the right data plan.
Only your wireless carrier can access and manage details about your account. If you need help finding your wireless carrier's service page, use the Apple carrier-support article or an online search engine.

If your carrier confirms that there's no issue with your account or network, but you still can't connect to a cellular network, contact Apple Support.
If you see No Service or Searching on your iPhone or iPad
Cheers!