I don't get it. If the collect call from A to B is accepted, B pays the cost of the call. In your scenario B instead calls A directly... and B still pays the cost. Where's the savings here?
(And there's a pretty clear downside to this. What if it's an actual emergency from a different phone than the standard. E.g. the only time I can remember answering a collect call, it was my sister calling from a foreign hospital after a serious accident. Trying to call back at a different number wouldn't have been great. I guess you could have a protocol involving multiple collect calls, and hope that there's no record that the first one was rejected.)
I made a collect call (~several states away) home when I was a kid and didn't have a cell phone. I forgot all about that. I feel old now. I remember my dad had to accept and kept it short to reduce costs even though I'd been away for weeks.
(And there's a pretty clear downside to this. What if it's an actual emergency from a different phone than the standard. E.g. the only time I can remember answering a collect call, it was my sister calling from a foreign hospital after a serious accident. Trying to call back at a different number wouldn't have been great. I guess you could have a protocol involving multiple collect calls, and hope that there's no record that the first one was rejected.)