[username190]

> It is not just "old" or 3G-only phones, it is any phone that is not explicitly on their whitelist.

This is correct. The whitelist that they're using specifically is here[0].

Some phone representatives will claim to people that they need a "5G Phone" - this is misleading, either on purpose (because the rep wants to increase their sales figures), or accidentally (because the rep isn't well trained on how to handle this situation).

AT&T will provide alternative phones for free, but they usually aren't great. Last I heard it was an iPhone SE (2020) for existing iPhone users and a low-to-mid range Android phone for existing Android users.

[0] https://www.att.com/idpassets/images/support/pdf/Devices-Wor...