This product link is to a headphone jacked input device that allows you to use your phone running a multi-track application. You can use it with the iphone with Garageband but you can also use it with Android apps apparently, since the connector has a headphone jack with the microphone input as well. Not sure if that was clear but if you're familiar with that then you'll know what I'm talking about.
== added 10-23-2012
This is also really cool. A four track app, which would be an alternative to Garageband.