Some people get creative with this signature. A few fun (if not necessarily business appropriate) examples found round the Internet include:
My parents wouldn’t buy me an iPhone so I have to manually type “Sent from my iPhone” to look cool
Sent telepathically
Sent from my laptop, so I have no excuse for typos
Sent from my smartphone so please forgive any dumb mistakes
I am responsible for the concept of this message. Unfortunately, autocorrect is responsible for the content
Sent from my mobile. Fingers big. Keyboard small.
iPhone. iTypos. iApologize.
How my heart sings 