Yup, there were several tricks like these! My father used to travel a lot and paying for roaming was expensive. So when he was available to speak, he'd just give a missed call at a fixed time and we used to call him from the landline (much cheaper). If we didn't get a missed call, he was busy.

I also remember while going to college, I had bus connectivity, but had to walk the last 3km or so home. I used to call either of my parents to come pick me up when I was around 15 minutes away from the bus stop.