Hello CoxB,
We understand you're getting an activation error to validate the SIM card when trying to restore your iPhone using iTunes.
If your iPhone can't be activated or an alert says the activation server is unavailable or the SIM card is unsupported, please see what to do If you can't activate your iPhone. If you continue to get an error message on your computer that says the SIM card isn't compatible or is invalid, please contact your carrier.
If needed, please see how to Remove or switch the SIM card in your iPhone or iPad for help with trying a different SIM card from your carrier.
If you've used your iPhone with a previous carrier and now you're trying to use it with a new carrier, we'd recommend making sure your iPhone isn't locked to your previous carrier. For additional details, see How to unlock your iPhone for use with a different carrier. Please note that Apple cannot unlock iPhones for use with a different carrier.
If you've confirmed there isn't an issue with the SIM card and activation policy for your iPhone, and you're still unable to restore your iPhone, please see what to do If you can't update or restore your iPhone, iPad, or iPod touch. Prior to restoring your iPhone, we'd recommend creating a current backup. If needed, please see How to back up your iPhone, iPad, and iPod touch.
If you still can't connect your iPhone to your computer, and you don't get a message about the activation server or SIM card, please see what to do If your computer doesn't recognize your iPhone, iPad, or iPod.
Cheers!