If you went to the keynote speech at the South by Southwest Interactive Festival here Sunday and found your cell phone not working, it wasn't your carrier's fault.
You can blame the SXSWi keynote speakers, Make magazine Senior Editor Phil Torrone and do-it-yourself electronics pioneer Limor Fried. During their on-stage conversation, the pranksters took the opportunity to show how to jam cell phone signals.
To demonstrate, they showed a spectrum analyzer measuring cellular activity in the immediate area. Torrone asked someone in the audience to call him and then turned on a homemade jammer. The analyzer's graph went haywire, and the call made to Torrone was dropped.