For what it's worth, people are still reporting 3G has not been fully shut down yet. As expected, AT&T has to replace cell equipment (seems to be replacing 3G/4G hybrid hardware with 4G/5G) as part of the shut down and that will take some time and vary region by region.
HSPA still working in Chicago IL suburbs - Page 2
HSPA still working in Chicago IL suburbs - Page 2