Not beeing economically able to actually buy the new iPhone, how can I impress my friends and family by posting status messages with the via iPhone postfix?
How to fake the via iPhone status message in Facebook
facebook;iphone
You would have to create a Facebook application.  When you sign up for a new application using the Facebook API, I think the name you give your application will be the name that shows up in the via part of the post.  I doubt you'll be able to register your application under the name iPhone, but you could maybe do one that is just as cool.See the status.set method on how to set the status using the API.  This requires some programming, but the API has libraries available for most programming languages.