I'd like to say that I'll schedule my day and work diligently, and I'm
willing to drop anything for an emergency.
But what's an emergency?
If it's something that “requires immediate attention”, then who gets
to decide what is “required”? For some customers, everything they want
is an emergency. In fact, some seem to intentionally implement things
without planning; that way when it doesn't work, they can call it an
emergency.
If it's something that can cause “real irrevocable harm” if ignored or
delayed, then practically anything in business could satisfy this.
Delaying almost anything could cost somebody some money. Spending more
money than you have (or not making as much as you need) can cause real
harm; people lose their goodwill, their jobs, go bankrupt, lose their
property, etc.
(My context is the telephone companies for whom I do technical work —
i.e., troubleshooting, configuration, and programming)
Mark Lindsey > 
Mark, because of my recent dealings with a co-worker to whom everything is an emergency (to the tune of close to 100 emails a day to multiple people as well as phone calls – all asking the same thing), I am on a quest for information on how to sensitively diffuse the matter and change the behavior. You have obviously given this some thought – so, a year after you post your comment, any grand insight you can provide me with. As an aside, I was brought up in RDU and really miss the place. All my fam is still there so I try to visit as often as possible.
It sounds like the person your working with really wants a team-mate sitting right next to them, working on all the same tasks.
Here are the only things I've come up with:
— Work on these “emergencies” as early as you can, but no sooner. You have to decide for yourself what other work must be done so you know when you can drop everything for the “emergency”. Having this mental limitation is important (though it requires a lot of self discipline).
— Match the requester's level of commitment. One policy my company uses is that, if you want work done immediately, you must stay on the phone with me while I do it.
— Figure out how to impose some cost on the requester for immediate attention. If it costs you the distraction, then it's got to cost them the distraction.
— Find a palatable way to set aside some do-not-disturb time for yourself. You may need some time when you can really shut down instant messenger and hit DND on the phone, and stop checking your email. Unfortunately, for some people, the only way to do this is to work after normal business hours. (DeMarco and Lister's book “Peopleware” talks about this at length.)
— Take a professional's approach: keep a calendar. Consider putting urgent requests on a calendar. “I can work with you at 4pm. Is that OK?” I've found that designating a specific time of day when I handle all of the tiny ad-hoc requests can work. The requester doesn't have to way too long — just a few hours — and he knows that he'll get your undivided attention at that time.
I don't do all of these all the time. But they're useful.