First they have started warning users who have not provided a mobile phone number that their Facebook security is low, and the first step to increasing their security is to provide that mobile number. This does boost security, as people tend to have only one mobile phone number, and a number can only be associated with one Facebook account. As a result, Facebook will have the the most detailed information available on every person who uses SMS messaging and web-enabled mobile phones.
The second move is a more recent change where they have removed the “suggest to friends” feature on pages, and replaced it with a “subscribe via sms” selection. This limits the ways business pages can be shared virally. No longer can a brand suggest to their fans that they share the page with their friends to build audience. As a result, more brands are pushed toward other forms of Facebook marketing like advertising, which typically has an abysmal click-through rate unless you offer something appealing for every click.
This change also encourages interest in alternative ways to reach the massive Facebook audience. Nothing encourages an appetite like having your dinner taken away. While online marketers are still trying to figure out ways to drive audiences to their Facebook pages, Facebook is cooking up an opt-in mobile marketing platform that dwarfs every other platform in both size and segmentation.
Facebook is constantly tweaking and experimenting with their user experience, and I can't tell you with any certainty where this is leading. Only Mark Zuckerberg know's that, and he's not talking. But these changes indicate that Facebook is very interested in connecting your mobile number to your other account information. It also serves as a poignant reminder to businesses that use Facebook as a marketing platform that when we're playing in their sandbox, Facebook can change the rules whenever and however they want.