Standalone GPS was clearly a killer, killer app. People said so with their wallets, forking out, in many cases, three or four times more than they paid for their cell phones in order to park a Garmin, Magellan or TomTom on the dash. Even now, the cheapest Garmins you can get at BestBuy run above $150 -- which many cell phone users would consider expensive because they are accustomed to subsidies from the carriers.

Since 2005, Garmin, the segment leader, has recorded revenues of $10 billion. The majority of those dollars came from sales of the Garmin personal navigation devices that can be most easily supplanted by Google Navigation, the search engine giant's recently released free turn-by-turn navigation software that works with voice requests spoken in normal syntax. (Garmin also sells into aerospace and a few other commercial vertical segments). I spoke a little bit about this in my previous post on the topic, but after thinking about it more, I realized that Apple truly needs to respond in kind and pronto.

Why? Because people have already made it clear that navigation is a killer app worth paying for. If they can get it for free on a phone running Google's (GOOG) Android operating system from Verizon (VZ), T-Mobile or even AT&T (which will also carry Android phones alongside Apple's iPhone), that should drive significant sales. And from a personal standpoint, as a longtime Apple user, I can relate to this sentiment.

Suddenly, the Garmin Feels Like a Horse and Buggy

I spent yesterday driving around Silicon Valley. I had a Garmin on my dash because I had not been willing to purchase the GPS apps from the iPhone store. There were enough user complaints about the apps crashing to scare me away and my iPhone runs out of battery charge fairly quickly -- plus, I like to be able to answer my phone without shutting off my GPS, a problem with the iPhone and its inablity to run more than one application at a time.

So there I was, at each stop, tapping away at the touch screen to enter a destination. First, input the city. Then the street number. Then the street. While I understand how to do this, now that I see I can do it with a single easy spoken sentence on using Google Navigation, I feel like I'm driving a horse and buggy while a guy with a car is in the other lane, chirpily rerouting midstream to hit an In-n-Out Burger off the 280 without breaking stride. (God help you if you need to input a new destination on an old-school GPS while driving.)

Would I buy an Android phone right now if I were not locked into an iPhone contract? I am not sure I wouldn't. For the millions of iPhone users -- not to mention existing customers of Verizon, T-Mobile, and other carriers who could easily upgrade to an Android phone -- this type of decision used to be academic, driven by Apple's amazing iPhone app store. Perhaps the app store has changed the game enough to make the addition of Google Navigation to the marketplace not such a big deal. But somehow, I doubt it -- and I've got 10 billion reasons why.

Alex Salkever is Senior Writer at AOL Daily Finance covering technology and greentech. Follow him on twitter @alexsalkever, read his articles, or email him at alex@dailyfinance.com.