How to get “green bubbles” texting to an iPhone user?

After all this online drama over something as silly as green bubbles, I just discovered their power. I had a brief power outage and apparently my cell provider had degraded service, so I had no data and text messages didn’t go through. Then I tried a green bubble conversation and it worked.

SMS worked, when data and iMessage did not. So how can I do that on purpose? I don’t know if this is a normal occurrence but the next time I have degraded service with no data, does anyone know if there is a way to SMS to fellow iPhone users?