If phones, propane, and explosives are combined, they could add up to a remotely detonated Fuel-Air-Explosive thermobaric weapon.
http://news.usni.org/2013/10/23/beirut-bombing-30-came-peace
Check out # 14 and # 15.
There are 3 - 4 articles of related info on Missouri, especially the post #14 here, that combines cell phones, propane, and explosives in a credible threat.
Thanks, anonymous. Good catch.