A few hundreads I think? Though I don’t know how many are part of this working group. It’s open though so you or anyone interested can join.

There’s also this one: https://fedidb.org/

I heard that Google is about to drop support of their older chromecasts. (You might want to look into this to confirm though)

Even better is to talk about phone carriers, because people seem to know those better than emails these days. “Just because your phone is using Carrier A doesn’t mean you can’t call your friends on Carriers B and C”

Eventually, Facebook and Twitter copied the feature, so Google+ lost its advantage.