I get quite a few to my mobile number, mostly during the day. Generally quite easy to spot and ignore, but I've found during a tough day at work if they call when I'm not busy they can be quite cathartic.
I like to engage with the caller (I mostly get actual calls from humans) and see how long I go before they hang up on me. Polite ones I just waste their time, less polite ones get an unleashing of all the rage I can't let out to customers. I even have a set of notes with good one liners to use since I always struggle to remember them in the heat of the moment. Things like :
"You're a polip on the arsehole of humanity"
"Records, what records? Do you mean the phone book and a magic f**king eight ball?"
"There's only one person who'd had an accident... your mum... 9 months before you were born."