Well, you're right, but fear as a marketing tactic is used to sell many other things than cell phones. It's a strong emotional motivator. Are you aggravated that fear is used to market products? Seems as useful as getting aggravated at people who get aggravated over the piddling annoyances which abound in human society.

In an "emergency" (yes, the meaning of the word has weakened over time; welcome to the wonderful world of language), a cell phone can be useful but probably not necessary. Just because something isn't necessary doesn't mean it might be a good idea to have it around. In a flat tire "emergency", a tire pump is pretty useful when compared to the hassle of walking the bike all the way back home. There might be some rare situation where a tire pump will help in a true emergency, like a cyclist fixing a flat in order to ride for help for a fellow cyclist in need of immediate medical attention. There might be some situations where having a cell phone could save a life. With that in mind: Helmets: Essential?