Speed dial #2 on my cell goes to my office phone - makes checking voicemail easy. And when the guy in the next office comes over to tell me about some damn facebook game he's playing now, I can fidget with my phone, hold down the number 2, and boom - my phone rings. "Oh sorry man, I need to get that."
Of course, if he ever notices that it's always the same number...
And as a bonus, I change the name from "Work" to "Santa" during christmastime. Scares the hell out of a kid throwing a tantrum when I threaten them with a long distance call to the North Pole.