The marketing only mentions Magenta plans, but the FAQ at the bottom of this page lists several other plans that are also eligible including the One plan which I believe was the top tier plan when they first rolled out the Gogo partnership https://www.t-mobile.com/benefits/travel/in-flight-wifi

Note there is a difference in the older/lower tier plans as they’ll only get 4 flights of full-flight WiFi per year, but will continue to get 1 hour of WiFi + unlimited messaging.