IIRC, ATT requires IMEI added to their allowlist to be permitted on their network. I suspect this will not work.

There may be some plan related limitations if you’re swapping from a smart phone to a “dumb” phone. That’s something that’s best to speak with an AT&T rep directly about.

As for the SIM card, yes you can walk into a store and request a physical SIM. There should not be any charge for that as you’re already a paying customer. Do not let anyone else fool you otherwise. Source: I used to work with cellular devices and am familiar with most AT&T policies.

Also, avoid AT&T franchises. When you walk in, simply ask if this is a corporate location. If they tell you no, I would try elsewhere.

Thanks y'all, looks like I'm boned until I get a pixel

Depends on your carrier and plan. Even if you swap the SIM, they might lock service to the IMEI. You'd have to check your plan.

You might just open a second line on a pay-as-you-go plan, so that you only pay for it when you use it.