We have been diligently researching the Facebook switch on Friday from FBML to iframes. Our advice? Don’t panic. Static FBML will be around for awhile.
All this move changes is that developers and designers now need to know HTML and have access to a hosted site in order to make custom applications and graphics for your Facebook page. Most page owners don’t realize that this is simply a change in how the coding of a Facebook app (i.e. a custom page) works. It's a slow phasing out of Static FBML, Facebook's proprietary application that allows users with little coding experience create custom tabs Facebook Pages.
With an iframe application, the main difference is that content must now be located within an HTML document that is hosted outside of Facebook's servers—usually, your own website (although they can and should be hidden). An iframe is simply HTML code or "inline frame." Basically, customs apps will now be a hosted "web page" layered on top of your Facebook Page. And your designer will need to know HTML.
There is already a lot of hype surrounding this change, and a lot of companies are trying to make money off of it, such as Wildfire and Involver, to name a few. Don't buy into the propaganda. Remember that “Free for 3 months” is not ultimately free.
In fact, there’s even a possible SEO downside to switching to iframes. At present, search engines do not crawl content within iframes, so anchor text links on your existing FBML tabs will not be crawlable. Unless something changes, iframes have absolutely no search engine value, and FBML does.
Your existing Static FBML tabs (like welcome pages and contests) will be fully supported by Facebook for a while. They can still be edited or replaced with new FBML code. No page owner with FBML-based apps needs to panic. When your current FBML apps no longer serve your audience, that’s the time to look into iframes. Right now, the cost of recoding into HTML and adding monthly hosting fees are too high to justify a switch.
For the near future, there is no reason we can see to upgrade existing static FBML tabs to iframes. Rest easy for now, Facebook friends.