Cryptome.org (
mirror) has some interesting information on the types of systems Bush is alleged to have used. Correspondent "J." explains how they work:
The frequencies for these units are very well known, and someone can sit outside many concerts with radio monitoring gear and listen to the assistants reading the words to the songs to the musicians, coaching them what to say, and quite often someone can sit outside a comedy club and listen to one-liners to cue the comedians and entertainers. Around political events these types of systems are very, very popular as the politician can have a half dozen members of his staff feeding him data, thus creating the illusion the suit has a clue of what he speaks.
When the president visited Boston back in March 2004 he stayed at the Park Plaza Hotel. The signal from the system he was using could clearly be heard 1500+ feet away, and one of his advisors could be heard doing voice checks and then feeding him data about the school he was about to visit.
While I was cleaning my tinfoil hat it occurred to me that if this fellow could listen to Bush's advisor feed him info, there's no reason why an enterprising Kossack from Tempe, Arizona, couldn't do the same during the third presidential debate (other than the very real possibility that Bush isn't using an earpiece). Interested parties can find a list of possible frequencies
here.
Jamming a frequency - even one allegedly used to coach the President while he's on live TV - might be illegal, so I don't recommend doing that. I will say this much: cutting the President off from his (alleged) helper while he was (allegedly) debating Kerry would result in some hi-frigging-larious television.
Disclaimer: I know there's no proper evidence that Bush has been wearing an earpiece and I have no idea whether the cryptome.org information is accurate. It's still fun to speculate.