Interestingly enough, a retro rotary phone lends itself well to iPhone docking. Plus, building one yourself looks to be a fairly simple procedure (so long as you are willing to cannibalize a speaker dock).
According to the project page, a version with a microphone on the handset is also in the works along with a compatible iPhone app. That would make it possible to use it for actual phone calls—kind of like the commercial retro handsets that have become so ubiquitous these days. [fonejackerhacker via Boing Boing Gadgets via Hacked Gadgets]