As usual, my e-mail column on targeted cell-phone ads last week triggered a huge volume of reader responses. (I get the feeling that a column on shoelaces would trigger a huge volume of reader responses.)

A surprising number of readers -- a bare majority, in fact -- were enthusiastic about the purely hypothetical program. (To recap: The F.C.C. is mandating that cell-phone carriers develop location-tracking technologies that can pinpoint your phone in emergency situations. A U.S. Sprint rep had been chatting with me about the possible marketing uses of this technology: that as you walked or drove by certain shops or restaurants that you'd selected on a Web site, discount offers would appear on your phone's screen.)

Their enthusiasm ran along these lines: "It's about time that someone pointed out that, in fact, targeted messaging, when used properly and *with permission,* can actually improve a person's experience with technology."

It wouldn't have been hard to predict, however, that many more people would be troubled by the proposal. "I cannot believe you would for one moment ponder the value of MORE JUNK MAIL, now delivered to a cell phone," wrote one person. "I am bombarded with enough junk from the WWW already that my portal home page looks like Times Square. I get enough telemarketing calls to choke a trunk line. And now you suggest that I would get value knowing that the pizzeria I am passing on my way to the health club is going 2-for-1 on slices at 800 fat-laden calories a pop?"

These readers apparently missed the fact that the marketing scheme I described, unlike TV and Web ads, would be strictly optional. If you chose to "opt in," you'd get a few bucks off your cell-phone bills (plus the discounts themselves) -- but if not, you'd remain ad-free.

Another reader wrote: "If cell-phone companies can identify your location, how long will it take before all your habits are tracked, compiled into advertising lists, and sold to the spammers?"

I guess that's theoretically possible. But what does that have to do with the E-911 program? If Sprint and other carriers wanted to sell its customer lists, they could do it today. (Why don't they? Might have something to do with trying to avoid infuriating their customers.)

A number of readers were especially upset by the notion that these discount offers might use up your monthly airtime. I wrote back that we're talking about tiny text messages appearing on your screen -- not actual phone calls. Still, I called the Sprint guy for clarification. He didn't know who'd pay for it, mainly because all of this is purely hypothetical and subject to a lot of user testing.

That's an important point: E-911 is a long way off. Sprint now sells the first G.P.S.-enabled phone, but it doesn't do anything special until the cellular network equipment itself is upgraded. Right now, only one state offers such upgraded gear (Rhode Island, which is so small that Sprint had to upgrade only a single station). It will probably take two years before all carriers offer the E-911 service nationwide -- for better or for worse.

Visit David Pogue on the Web at DavidPogue.com.

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