> For example, a bundle may provide 200 minutes of calling during a 7-day period for a discounted price. To avoid losing unused minutes, we learned that as people near the end of their bundle’s time period, some use available minutes to call back unusual numbers in their incoming call-log, which they had not answered.

This probably explains the reason for the accidental social ties.

I lived in a country where mobile phone calls were expensive relative to wages. Much of the time you'd receive a call that only rang once. The caller would hang up after only a single ring. This signalled they wanted to talk to you but didn't have enough "talk time" left. If the caller was a contractor or someone on your payroll, they would almost always employ this tactic to keep their costs down.