(CNN) -- We're reviewing two $99 turn-by-turn navigation applications for the iPhone, TomTom and Navigon. Yes, that's right, a $99 application for your phone to take the place of a stand-alone device that doesn't cost much more than that.
First off, if you plan to use your iPhone as a turn-by-turn navigator, you'll need some sort of mount that keeps it in constant view of the sky (and to keep you from wrecking your car while trying to look at the screen).
As I was driving around downtown Atlanta, Georgia, both applications spent a good amount of time telling me they couldn't get a good GPS lock, even after I dug out a window mount from my box of bits and pieces.
Both of these applications have most of the features you would expect; basically, put in a destination, and they tell you how to get there.
Both can save favorites; both even have a walking mode (though I haven't played with this enough to recommend it).
Both take up a ton of space, and both currently cost $99 (though the Navigon had an early buy-in price of $69).
Navigon also has the TomTom beat on features: An early update added text-to-speech, which means Navigon's app says the street you should turn on and not just "turn left."
Navigon also just released a $24.99 (intro priced at $19.99) upgrade option that will give you live traffic information.
I've asked TomTom about possible updates, and they say they're considering what features to add.
My early call for the best interface goes to the Navigon app.
And this held up the more I used both of them.
I find it much more intuitive; things are where I expect them to be.
When I want to change something on the TomTom, I often find myself repeatedly clicking through the categories, trying to find a particular setting. The Navigon's interface is better for me.
An example of the interface conundrum: When I got the software, I hit the "home" icon to tell it to direct me to my house. Of course, I hadn't set that address up yet. The TomTom told me I had to add it from the "manage favorites" menu; the Navigon app asked me if I'd like to add it and let me do it right there.
Overall, my preference for the Navigon app holds true. I like the look and feel of the maps better, how it switches to night view automatically and its on-screen and voice alerts.
The TomTom, by comparison, seems very low-end -- the maps aren't as nice -- and without text-to-speech, the voice prompts fall short. I like to know what street I'm looking for without looking at the screen.
The big feather (at an additional $120) in TomTom's hat is its car kit.
Essentially a dock designed for your car, the device adds power, a bigger speaker and a better GPS chip.
The bigger chip should help the application be more accurate with your location and provide quicker prompts when you need to turn.
But at that point, you'll have spent more than $200 on a navigator that uses your iPhone as its brain.
I just got my hands on TomTom's dock, and although it's nice and should improve the GPS performance, I'm not sure it's worth an extra $120.
So, down to brass tacks: Is it worth it to pay $99 for a smart phone navigation application when you could buy a stand-alone model (likely with a better GPS chip) for the same or not much more?
Personally, I like having it all on my phone, one unit that does everything (and I probably won't forget it in the car to be stolen).
Other people will probably rather have the stand-alone.
And of course, there's a big caveat: Google.
The technology powerhouse has a turn-by-turn application in beta for its Android 2 operating system.
It's free for phones that run Android 2.0, and word is that they're in talks with Apple to get it on the iPhone (word that brought a big hit to the stock of both GPS giants, Garmin and TomTom).
Who knows what's in the future for these apps? But I'll bet they'll come up with something to remain at least somewhat viable.