Just saw this article at Rocky Mountain News on cell phone jammers being used in a church in Mexico.
http://hosted.ap.org/dynamic/stories/C/CELL_PHONE_JAMMERS?SITE=CODER&SECTION=HOME
Reporters noticed they couldn't phone their editors.

Not to be paranoid, but is it possible such devices could be used strategically (though illegally) to disrupt poll watching on election day?

Here's a quote:

"Purchased for about $2,000 each, they can be turned on by remote control and emit low-level radio frequencies that thwart cell phone signals within a 100-foot radius.

Users get a "no service" or "signal not available" message on their cell phones.

Although Mexico has no law against the devices, the private use of cell phone blockers is illegal in the United States and most Western countries.

But the tide is turning."