[Jach]

Correlation may not boolean-logically imply causation, but it's evidence of causation. http://oyhus.no/CorrelationAndCausation.html

The actual cases I've seen (some linked on this page) are of specifically targeted individuals having their phone receive a command to turn into a bugged phone. I don't think all phones are bugged by default. This fits with Snowden wanting people around him to sound-proof their phones as they might be targeted.