Totally agree with BombDog and CMC55. When my phone "expanded" and self destructed and I took it into the Apple store I was told by a genius that this was a "feature" of the phone. i.e. as Lawrence Finch has pointed out this is the way that Apple prevents the phone from igniting and REALLY doing damage to life and property.
Fine.
But how about telling us about this wonderful feature BEFORE we buy the phone? If I had known that at approximately 2.5 years my $700 device would self destruct I might have made a different decision about buying it.
If I had been told beforehand about this excellent feature of the iPhone 3GS I would have been very careful to have the battery replaced after 2 years. A statement in the manual, or on the packaging such as: "WARNING: battery MUST be replaced in 2 years to avoid total self-destruction of this device."
The big question I have is: why is Apple not disclosing this very important feature of their phones?
Now I have an iPhone 5 that is about 1.5 years old. Is it soon going to self destruct? How will I know? Apple is not telling us, so how can we find out? Is it the responsibility now of all owners of Apple products with enclosed non user servicable batteries--which are now in tens of millions of devices including MacBook Airs, countless iPhones, and iPads--to search online for discussion threads such as this one to know if we have to replace the batteries? Or do we just wait for these devices to "expand" safely, and nicely self destruct without catching on fire?
Or should it be up to Apple to tell us when the battery ought to be replaced?
In all my life of about 50 years of owning countless electronic devices from my first 6 transistor radio to my current MacBook Air I've never had a product that self-destructed BY DESIGN after 2.5 years. And with no warning. To me and many on this group the responsibility should be with the manufacturer to explain clearly up front when and how to change batteries in their products if those batteries are designed to and known to destroy the product only 2 or 3 years after the product is purchased.
Now THAT seems blatantly obvious to most of us. Why is it not obvious to Apple?