Deeper Reset than Factory? I have a Galaxy S7 which I purchased from Virgin Mobile a few years ago. Recently, because of international travel to Mexico and Canada I had it unlocked and now have an AT&amp;T account. However, when I traveled to Mexico, the roaming feature is grayed out and it never connected to a network. The SIM worked, connected to the Mexican network, in another Android, so its not the SIM. As a last resort I factory reset. The Virgin Mobil splash screen came up, so apparently some settings are still in ROM. AT&amp;T Tech Support verified a correct account configuration (roaming enabled)

Is it possible to reset this portion of the ROM?  I'm thinking the Intl Roam feature is disabled in the same manner that the splash screen wasn't blown away from a reset.

When I came back to the USA, the phone worked, but i had to manually set the data network access point.
Virgin mobile is a proprietary prepaid Samsung Touchwiz Android repack - So that portion of the rom is not configurable.

What I would do is reflash the phone to North American Unlocked S7.

here's an XDA link with instructions.
it might be a bit of a pain but it will solve your problem utterly, and debloat your phone as well... making it a better phone quite frankly...

https://forum.xda-developers.com/galaxy-s7/help/sm-g930p-to-sm-g930u-t3813580