If you've been following Apple-related news over the last 6 months or so you're well aware that the iPhone 5s is coming soon and will include a fingerprint sensor for user authentication. I expect Apple to leverage this in their marketing by promoting the 5s as being secure (the implication - and reality - being that Android is not as secure).
- iPhone 3GS: Speed
- iPhone 4s: Siri
- iPhone 5s: Secure