The Li-ion / Li-Polymer battery does make a nice loud "POP" when it expands (some call explode.)
I don't own a Iphone but my Aircard sitting on my desk had a slight expansion problem and I never sat on my aircard or exposed it to heat.
Here's a picture of it that might give you a good idea of how it could break apart the iphone.
http://www.homelandtechsupport.org/img_posts/595U_Battery_Face_View.jpg
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The Li-ion / Li-Polymer battery does make a nice loud "POP" when it expands (some call explode.) I don't own a Iphone but my Aircard sitting on my desk had a slight expansion problem and I never sat on my aircard or exposed it to heat. Here's a picture of it that might give you a good idea of how it could break apart the iphone. http://www.homelandtechsupport.org/img_posts/595U_Battery_Face_View.jpg