$5 Monthly with this background app.

visit: https://unity.wavenodes.io/?21fmr

This lightweight app collects telecom telemetry by measuring things like your internet quality. Telecom providers pay for these automated micro tests. Your personal info is not being sold.

It's currently in the testing phase, earning you around $3 to $6 per (old) phone per month. And more if you complete the optional active tasks.