An iPhone 4 exploded while on board an Australian Airlines regional flight from Lismore to Sydney. The incident happened while the airplane was making preparations for landing.
The iPhone's owner reported that his phone was getting very hot and started glowing red just prior to the incident and called a flight attendant for help who reportedly secured the iPhone and extinguished the resulting fire.
iPhones exploding are not a new phenomenon, in fact there have been several reported and documented cases in the past. All have been attributed to the battery overheating.