I correspond with an iPhone user and every few months my friend asks what the J in my message stands for. She sees the characters on the left on her iPhone, while what I see in Outlook is on the right.
Outlook's autocorrect changes the :) into a smiling face. The smiling face is the capital J in the Wingdings font. However, the iPhone doesn't have the Wingdings font. It uses it's default font and shows the capital J (or an L instead of a frowning face).
This problem isn't limited to the iPhone or email - any device that doesn't have Wingdings font will use their default font when displaying the document. While this can be a problem with any font, it's only an issue with symbol fonts because the characters are replaced with something else. (A J in TNR is a J in Arial, but could be any image in a symbol font.)
To avoid confusing my friend, I click Ctrl+Z to undo the autocorrect.