Didn't want to do that before, as it was $15 per day calling in the U.S.Interoperability between *all* brands sucks in my experience. I have one regular riding buddy on a Scala system and despite more than a few attempts we've never managed to get ourselves properly paired. We *almost* made it happen once but it ended up in some weird in-between pairing where it didnt seem like it had paired, but then a few hours later when he hung up from a phone call, suddenly I heard random coughing in my ears over my audiobook and after some confusion, realized it was him - when he hung up, somehow the com channel had opened. When we closed it, the only way to get it reopened was for him to take a call and hang up again.
Quite often if we're on a group ride together and need to chat at some point (he often tailguns, I often lead), I just call him instead - no bluetooth range issues that way either. Not ideal, but gets the job done.
The Cardo app is really slick for adding new groups or new friends to existing groups when they're also Cardo users.
I just changed from one Telus subsidiary to another, and now have free U.S. calling.
Phone can sit under the seat on a charger, so it's a good backup plan.