They usually phone on Friday, just a few minutes until I'm closing the shop.
Many years ago, whilst working for a certain mobile base-station manufacturer, I was banned from having a sign above my desk that read: "Your incompetence does not constitute my emergency".
The person who was most responsible (sales type fond of dropping by and giving us 4 hours worth of work at 5pm because he had all the forward-planning skills of a rabid ferret on crack) had apparently complained about my attitude.
So I generated a counter-complaint about his. He ws gone about 2 weeks later. I guess I wasn't the only person he'd annoyed..