At this time, I believe the only way you can export what you create in Band is via the headphone jack on the iPhone. Thus, you'd have to have some form of audio recording capabilities (e.g. tape deck) or an audio interface to get it into your computer. For example, if you had an audio interface (like a MOTU Ultralite), you could use an audio cable that takes the stereo signal from the headphone jack and connects it to your interface and then you could do a manual audio recording of what you created with Garageband. Once in Garageband, you could convert it to mp3 or make a ringtone out of it. Not the most ideal way of recording something so hopefully the makers of Band will come up with another solution with a future version, if possible or allowed. It would better if you could get the audio to come out of the port on the bottom of the iphone instead of the headphone jack, since the audio quality would be better. But I guess ideally we'd want the Band program to be able to create a high quality audio file that can be exported out of the iPhone and later converted to mp3 or whatever format needed. Also, it would be nice to have a midi export as well. Midi files would be smaller to export and you could then use the Band program as a scratch pad for jotting down musical ideas anywhere/anytime that you could export and work on later with better software. That would be nice.
i use a $2 cable that i got at radio shack, it has a headphone jack at one end which i plug into the ipod touch, and at the other end, i plug into the computer and into a audio recording program, such as adobe audition...it works and from there i can encode it into an mp3