Orbot needs wifi only option for Relay.
Orbot for Android has a Relay setting. And I would love to use it to help. However, you might want to enable as a default ACTIVE if on WiFi. That way everybody who downloads it can help when on WiFi and not while on a limited mobile phone plan.
Or for those who have limited data plans, they can set the Relay to be on when WiFi is detected.
And if On when WiFi is detected, the phones can also serve as your Exit points. Furthering the cause.