Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Is there a GPS service I'd have to purchase to get this to work?
Document: This was my first GPS ... . Not only is the etrex durable andsolid, but it's really tiny! It easily fits into the palm of yourhand with buttons on the sides. The menus are great to work with and make using most any feature of the GPS as simple as hitting two to three buttons. I'd highly recommend this GPS for any one who enjoys the outdoors and is looking for a small, affordable GPS.
Upgrading the receivers' firmware did nothing to help the accuracy.Granted, my experiences with this receiver probably won't matter that much to most of those who will purchase this unit for tasks such as finding your way around while camping, hunting and hiking. For those uses, this unit will work just fine.
And for more money, you can get more bells and whistles in the higher end eTrex models. The large screen is both a plus and a minus--a plus in that it's very easy to read and you can easily navigate the menus on it. A minus since it can be damaged, and a large LCD screen will not work well in extreme cold. The bottom line is, if you want to get started with GPS navigation, the eTrex is a friendly way to get going.
I work as a structural geologist, a job that requires spending long periods of time hiking around the deserts of Nevada. For obvious reasons I was keen to get a GPS reciever that was small, reliable, and not too expensive (one never knows when one might accidently set it down and walk off - "GPS find thyself!"). The Garmin eTrex proved ideally suited to my specifications and proved to be perfectly equipped for my purposes.
One thing, get yourself some rechargeable batteries, once hooked you won't want to turn it off.I just wanted to share while I came back to Amazon to upgrade to a ETrex legend (I'm hooked and want a map and panning) and thought I'd add my 2c in to someone getting their feet wet.
This unit has done all it is supposed to do for me and I use it almost everyday for at least 8 hours a day. I use it with a laptop and mapping software for traveling with a laptop. I'd hate to imagine doing what I have to do without it. It can get you out of some very rural areas fast. As far as hiking or something in that area I couldn't make any comments because that is not what I use it for.
I own three of their products and this is the worse one for not living up to what they say it will do. The best one out there for tuff service  is the GPS 45 version.
This GPS offers MANY great features, including ability to interface with APRS Ham Radio position broadcasting. ( reason for purchase )
I purchased the Venture Cx and it stopped working. Called customer service and they said to send it back. Sent it out on Monday and had a brand new one delivered on Friday. Also included was a free car charger. That is what I would call customer service! The Venture Cx has been a great GPS!
I recently bought an E-Trex primarily because of the low cost of the unit. I am very satisfied with my purchase. I am surprised how rugged it feels and it appears to have a little more knock-ability than some other handheld  GPS units I have used.
Answer: No. It tracks satellites.