Cell phone users generally don’t know that they are being jammed. The only clues are phones that report no service or no signal from the network. Ways to bypass a cell phone jammer are to make calls over a Wi-Fi connection or make calls using Skype.
Recently, a Philadelphia man fed up with fellow passengers who yak loudly on cell phones during bus commutes admitted to using a cell-phone jammer to create a “quiet zone”. Headlines of this story and “cell phone jammer” as a top 10 Google Trends search prompted the Federal Communications Commission to post this document on their website which states that cell phone jammers are in fact illegal in the U.S.