Think you're in the market for a satellite phone? Think very carefully.

Satellite phones can literally be life savers. But don't consider purchasing one with the thought that you'll be able to call anyone from anywhere you go in the backcountry of the National Park System, or any other remote area, for that matter.

They're not cellphones, tying into a system of cell sites (aka towers) to relay your calls. They, as their name implies, rely on satellites to put your call through. And in some locations, the landscape simply is not conducive to good satellite connection.

Since spring I've had a SPOT Global Phone to test out in the field, and it's had decidedly mixed results. My first use, in late May, came during a float trip down the Green River through Dinosaur National Monument. The next opportunity arose in mid-August during a paddling trip in Yellowstone National Park.

The results? The clarity was incredible. When I was able to get a call through.

Conversations with my wife were as clear as if we were sitting at the kitchen table in a quiet house. Much, much better than the sometimes scratchy reception you can encounter on a cellphone.

But that clarity came with two critical caveats: 1) Satellite phones aren't well-suited to deep canyons, such as the ones the Green River cuts after it passes the Gates of Lodore on its way south through Dinosaur. 2) The phones rely, as noted above, on satellites, which come and go across the sky relatively quickly in terms of phone conversations. But then, the purpose of a satellite phone is not for conversations, but to summon help.

A SPOT representative explained to me that the satellites that the company's phone connects with come and go every 15 minutes, and so how long your call might last depends on when the phone latched onto a satellite. It could be 15 minutes long, or 30 seconds. Toss in tight parameters, such as canyon walls or even Park Avenue walls in New York City, and odds of a connection become even more iffy.

With the deep canyons cut by the Green, there was literally a small window of sky overhead that the phone's antenna could point to, making it hard to lock onto a satellite that might traverse that window in a minute or two. As a result, there were times on the trip when I simply couldn't get a connection, and times when the connection I landed quickly, and abruptly, was cut as the satellite passed out of range.

Now, out on Shoshone Lake in Yellowstone in August, deep canyons were not an issue. The thick lodgepole forest rimming the lake could have posed a problem, but from the shore it was easy to place a call and the reception was outstanding.

As for the phone itself, it's small enough to stash in your pack, measuring just over 5 inches long, a bit over 2 inches wide, and 1.5 inches deep. Extend the antenna, which you must do (and be sure it's pointing skyward, not over your shoulder), and the length roughly doubles.

The screen is small, about an inch wide and just over a half-inch deep. The shell is plastic, and so you don't want to drop it, or drop anything on it. Standby time with fully charged lithium batteries is 36 hours, or you can talk for four hours. There also is a "minute alert" you can set to alert you when you're running out of minutes.

Now, along with considering where you might be using a satellite phone, you need to consider the price. The SPOT Global Phone, outside of special deals, sells for $500. And then there are the monthly data charges that quickly drive that price higher. They start at $25 a month, which gets you 10 minutes of call time with additional voice minutes running $1.99, voice mail $4.99, and "express data compression," which you need for emails, another $4.99

The plans, which require 12-month contracts, peak at $1,800 a year. For that you get unlimited minutes, voice mail, data compression, everything you'll need out in the field. You also can get a six-month plan for $300 that includes 200 minutes of talk time. (There is a $50 activation fee for all plans).

The relatively high costs are the result of satellite technology. It's not cheap to launch a satellite, or buy communications space on them.

For the occasional backcountry traveler, the cost of this phone could be considered exhorbitant and out of the question. But measured against the cost of a 0-degree sleeping bag, a four-season tent, or even a collection of boots, rain gear, and warm clothing, the cost also could be considered reasonable, particularly if you ever run into trouble in the backcountry.

If you head frequently into the outback, and like knowing you most likely can reach someone if you encounter an emergency, the SPOT Global Phone is definitely worth considering.