The iPhone this week got a new entry in the fast-moving category of GPS software: MotionX-GPS Drive is by far the least expensive of the half-dozen alternatives, with a "holy cow!" low price of $2.99, with an annual subscription of $25. It's a heck of a lot cheaper than any of the alternatives.A half-dozen vendors, including TomTom and AT&T, have come out with iPhone nav apps. These are relatively big-ticket purchases; the subscription-based AT&T app is $10 per month. Other apps have one-time purchase prices ranging from $35 for CoPilot NA to $100 for the TomTom app.

Like the AT&T app, the MotionX-GPS Drive (iTunes store link) is a networked app, it doesn't store maps on the device. That has several advantages, chief among them that all the map information and points of interest are up-to-date. If a street recently got made one-way, or a new restaurant opened nearby, the MotionX-GPS is more likely to know about it faster than an app that stores its data on the iPhone.

Also, the MotionX app is likely to be much faster and more responsive than competitors that store their data on the device; I have used the others and they're all slow, as they access enormous maps.

Likewise, the MotionX app will take up less space on your device; the competitors take up around 1.5 gigabytes, and require twice that to install, the MotionX app requires just a few megabytes.

However, there's a trade-off to storing data on the server, and it's a big one: The app requires a 3G or EDGE connection to plot out your route. It stores the route locally so you don't need a GPS connection every moment you're driving, but if you make a wrong turn and you're in a dead zone, you'll have to wait until you're back online before it recalculates your route.

I haven't tried the MotionX software yet, so I don't know how much of a problem that will be. If you routinely travel through dead zones, then the MotionX software will be a problem for you. But in that case you probably hate your iPhone anyway, so you are not in the target market for this software.

The vendor boasts that the software was designed specifically for the iPhone, with a native interface. They make a big deal out of that. It's true that the competitive software was ported to the iPhone, and look and act differently from other iPhone apps, but that's not necessarily a large problem. I find the Navigon app, for example, to be quite comfortable to use on the iPhone, even if the interface looks a bit different, while the TomTom has a very iPhone-like look and feel.

The vendor says the software is designed for walking as well as driving; competitors are really focused on driving. FullPower includes shortcuts and pedestrian-only paths in its maps; it seems to have been designed for city-dwellers who do a lot of walking in town as well as driving.

MotionX-GPS Drive is a product of Fullpower Technologies, which makes one of my favorite apps, the free MotionX-GPS Lite. I use that app occasionally to measure my daily walks for exercise; it tells me how far I've gone and how fast I've walked. The app also has a $2.99 Pro version, which lets you store routes that you've walked, upload results to their servers, share photos, and more. It's really designed for mountain-bikers, hikers, rock-climbers, and other people who are much more active than I am, but I like it.

The CEO, chairman and co-founder of FullPower is Philippe Kahn, who founded Borland in 1983 and was its CEO until 1994.

One of the problems with GPS software on the iPhone is that it's expensive. $35-$100 is too much money to spend on software you might hate. But you can afford to try the Fullpower software; the first month subscription is included in the purchase price, and if you hate it, well, you're only out three bucks.

I've been trying out iPhone nav software , and hope to bring you mini-reviews here over the next few weeks. Spoiler warning: I actually think all of them are quite usable. My current favorite is the Navigon software (iTunes store link), but I think any one of them will easily get you from one place to another.

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