Not long after the Open Accessory Kit was announced, romfont posted a great set of instructions on getting this work with a standard Arduino:

A lot of people have been put off by the price of the reference hardware kit, which is roughly $390. What’s worse, they appear to be sold out until end of May, and Microchip’s cheaper ($80) alternative doesn’t arrive until July. So instead of waiting I decided to write a guide on how to get an ADK-capable Arduino for about $55.

Although romfont didn’t have an Android phone that supported the accessory libraries, follower did, and has confirmed that romfont’s hack works:

rancidbacon.com: Android Arduino Accessory

Update: follower has posted a stripped-down version of the DemoKit app along with a sketch that will run out of the box on the Uno! I gave this a try myself, though I had to use Duemilanove because my Uno is busy doing other stuff. In order for this to work, I had to use the new USB Host Shield Library from Oleg Mazurov that includes support for Open Accessory .