It’s $20/month (well, $21.64 after taxes and fees). And no, I don’t do anything for t-mobile. I enable network mapping
in the Helium Mobile app and every once in a while I claim the accrued mapping rewards and use them to pay Helium Mobile the bill for all of my family’s lines. We haven’t had to pay for our cell phone out of pocket at all this year (signed up in December) and have a couple hundred dollars in mapping rewards sitting there (with more accruing daily) to pay the bills for the next several months. Or I could just cash it out if I wanted.
If you don’t want to sign up, great. There is a fixed amount of mapping rewards each day, so more people signing up means less mapping rewards per person. More for me and my family.