[immibis]

(1) buy a true unlimited data plan (2) download and upload as much as you can for a whole month? Make sure it's something useful though - iperf is cheating.

Since it's true unlimited, they don't track usage. You can set your phone to a 1GB warning so the counter will always be displayed in your notifications.

[walthamstow]

I may be wrong but I believe uploads don't contribute to data usage caps. This is based on my experience using eSIMs for travelling.