Business models of Facebook

I have recently been observing where the posts of my friends on Facebook are coming from. This is proving rather interesting.

Some friends are posting "via Mobile web" others "via Mafia Wars Game" and some "via Facebook for iPhone". This leads me to wonder is Facebook earning money form e.g. iPhone or other suppliers. Facebook could e.g. try a business model of x cents per mobile phone. The x cents would be embedded in the sales price of the phone and the buyer would not be aware of having paid to Facebook. I have a Nokia phone and when pasting on Facebook my friends see "via Mobile web", which looks kind of dull compared with "Facebook via iPhone", which is nicely cobranded.

I also noted that Facebook is openly advertising its mobile applications with a "Try Facebook Mobile" icon, that is easy to click and proceed to become a mobile Facebook user.