According to Matt from 37signals the line “Sent from my iPhone” at the bottom of an email means this:

Let’s be honest. “Sent from my iPhone” really means “I’m not going to bother to proofread and correct this because it would take me an extra 30 seconds.”

I agree. I too use this line as an excuse to write a terse message and omit proper salutations.

However, I also think these four simple words greatly helped the viral growth of the mobile phone. Having early adopters brag about how they’re sending emails from their fancy new phone must have been an invaluable form of word-of-mouth advertising.

I think it’s safe to say that those four words first are a marketing technique and then a convenient way of letting your correspondents know that there might be a typo in your message. If not, the default line wouldn’t include the brand name.

I’m turning this thing into a rambling though. What I really wanted to share is a snippet of the much recommended book The Lean Startup, where Eric Ries shares a story on how Hotmail used a similar technique in 1996 to fuel their viral engine of growth.

But everything changed when they made one small tweak to the product. They added to the bottom of every e-mail the message “P.S. Get your free e-mail at Hotmail” along with a clickable link.
Within weeks, that small product change produced massive results. Within six months, Bhatia and Smith had signed up more than 1 million new customers. Five weeks later, they hit the 2 million mark. Eighteen months after launching the service, with 12 million subscribers, they sold the company to Microsoft for $400 million.

I find it incredibly intriguing how a few words can have such an impact. Maybe you do too.