The tech media, blogosphere and Twittersphere are abuzz over what Facebook will launch during its announced press event tomorrow in San Francisco.

Few doubt that it will be a new mail client. We speculated at our DMS conference and more recent rumors point to an internal “Project Titan.” It’s also been feuding with Google about data portability for e-mail addresses. Not to mention today’s event invitation includes its mail icon.

Speculation mostly comes down to features and touch points with Facebook’s social graph. What form will this take and where will it reside? Generally, I predict tight integration and a simple interface that lowers barriers for e-mail converts (and the colloquial “FMail”).

Stop Saying ‘Killer’

You’ll hear lots of “Gmail killer” claims today, but I’m not convinced that will be the case. Gmail users are pretty loyal and it’s a solid mail client. Gmail will remain the client of the tech elite while Facebook will be the mainstream client that disintermediates the incumbents that currently hold that title.

Of course I’m talking about Yahoo and Hotmail — behind the times and deserving of disruption. Rather than upgrading to Gmail, a Facebook Web mail client will compel users to leapfrog directly to the shiny new service that plugs right into their existing social graph.

Facebook will accomplish this with a much better product, but more important is its massive mainstream reach. It will also sweeten the deal with a prepopulated address book that maps to your social graph, and ties in to features like photos (currently the largest photo sharing site in the world).

Through all of this, Facebook not only ties together its growing list of social sharing assets, but also longer session lengths and page views. Here’s where Facebook could find considerable growth potential in the $2 billion it’s already making from display ads.

Another Brick in the Wall

As for the form it will take, users will likely get @facebook addresses (land grab anyone?) and the new client will be full-featured with POP and IMAP support for third-party clients like Outlook. But where will it otherwise reside: outside Facebook or inside (as it currently does)?

The former would be true to “mail client,” but the latter consistent with Facebook’s structure. It continues to lay bricks on what is looking more and more like a walled garden. Didn’t we all come to an agreement about a decade ago (think AOL) that this isn’t the way forward?

Very ironic that arguably the most successful media company in the world has reverted to that very model. We’ll have more detail about this particular brick after the announcement. Further out, we’ll add this to our talking points for the featured Facebook session at ILM:10. Stay tuned.