When I was a teenager, one of the local mobile providers had some plans where they would only charge you for a call after being connected for more than five sec

When I was a teenager, one of the local mobile providers had some plans where they would only charge you for a call after being connected for more than five seconds. One friend abused the hell out of this and started using it as "free push-to-talk" essentially. I had a plan with free calling time, so he would also sometimes call me, tell me to call him back, and hang up within about three seconds.