1) A long text from one person, which goes over the character limit and is thus sent as a series of texts, all received at around the same time.
2) Many people text you all at once, or in very close proximity, often referring to the same subject
3) Your phone buzzes when you receive an email, and REPLY ALL happens.
Other causes include telemarketers and Lots of people expecting a lot from you at the same time.
...6 New Messages
"That was quite the Phonesplosion"