Cell Phone Towers

I was driving from Holland, MI to Grand Rapids, MI yesterday and started realizing the number of towers along the highway. For some reason I started to count the number I saw from I196. Heading East twards grand rapids, I counted 17 towers. Of the 17 I think that at least 15 were cell phone towers. This got me thinking of what the regulations were on towers, and also what kind of frequency (number of) towers are needed for good cell phone coverage. Were all 17 towers used for Nextel, or cingular or any other carrier?

I have not done much research on this, but it did get my mind wandering. So I did a quick google for cell tower placement. What I found was a cool tool that lets you find all the tower locations. I am not sure what good this information is but you can check out the tool here (http://www.berkana.com/tower.php3).