I feel like it's a better deal economically to use the hotspot built into your smartphone. Your plan may already include hotspot data for free. And if it doesn't, then when you buy the hotspot for your phone, it sticks with your phone (it isn't tethered to your car).
But my guess would be to remove the tablet, unsolder the AT&T SIM, solder in your SIM, reinstall tablet.
It would be nice to hear from a Honda mechanic whether the AT&T SIM is tied to the tablet firmware or not.
If so, this won't work.
Another idea is a USB-to-SIM adapter.
Patience, it's a matter of time before someone with more time then me hacks into this and figures it out.