Hi Kate,
I took an exploratory, quick stab at this a few months back. Unfortunately I don't know the data that well and I only had an hour or two.
Here's the description I wrote up in March for my notes:
Downloaded some FCC ULS data for 'Utah' and made a crude attempt to convert it to a shapefile. I think it's supposed to be all the Utah FCC licensed transmitters including mobile phones, radio, tv, etc. Not sure how good this data is. Upon cursory investigation it seems to be missing the cell antennas in my neighborhood and seems to have some cell sites on buildings that are no longer there (Guardsman way armory near U of U for example). But it does have a lot of seemingly valid data too. For example, it has a bunch of towers that I can see on the imagery in the Wasatch and the Oquirrhs. The data also has points outside Utah despite the fact that I did a "geosearch" for everything within the state of Utah. Also, wasn't able to get a good understanding of the data dictionary for ULS to make out the field and attributes but I believe there is a height attribute in meters toward the end of the list of fields.
I'd take this as an example of what might be available and if we want to pursue it further, I think we should establish a contact at the FCC and have them respond to a more specific request for data and documentation.
FCC Universal Licensing System Database:
http://wireless.fcc.gov/uls
Download my test shapefile:
http://gis.utah.gov/index.php?option=com_docman&task=doc_download&gid=90
Let me know where you get with this. We (AGRC) would be interested in partnering to get this data layer built and updated periodically
-Bert