JPJ... youre right it works off cell towers.. you need this to make it work with sat signals. http://www.findmespot.com/en/index.php?cid=116
Its called spot connect.. it turns your iphone into a satellite phone via blue tooth. It was designed for emergencies for avid outdoors men away from a cell signal.
But the brush piles and creeks and available for download on the web at Ark game and fish. AGFC | Arkansas Lake Maps --- They have a lot of lakes here, but some are without the good info. Lake maumelle has a good.
For the creeks you need NHD data, which is provided by the USGS. But you'll need some kind of GIS/GPS software to convert it to work with youre GPS.
I'm a GIS/Cartographer and I make a map of every place I go. PM me for a map of a lake that doesnt have any data online. Or if you need something converted for your gps.

gregsmaps.com