To make a call to a persons cellular device, only allowing it to ring once and immediately hanging up. So that the person misses your phone call (and hopefully does not her the one ring), while at the same time giving the caller the ability to TRUTHFULLY say ... "I called you but you didn't answer"
"Why didn't I call you? I did call, you just didn't answer. Check your recent incoming calls, I bet I'm one of them! - Shadow Calling