Garageband on iPad: sharing 1 project between 2 iPads

Hello, all,

I posted this question in the iPad community, but it occurred to me that the Garageband community might be a better home for it.

Anyhow, I am hoping somebody can help me achieve what something that it strikes me that Garageband on the iPad should be perfect for, but which I just can't seem to figure out!

I am the guitarist in a band, and hoping to use my iPad to co-write songs with the singer, who lives in another town.

We can't always get together for writing sessions, but, since we both have iPads, I assumed that I could start projects by making some instrumental recordings on my iPad, and then share the project with the singer to add vocals on their iPad, and that they could then send the track back to me for further editing, adding extra parts to, etc.

This seems like it would be a great way to develop songs with a co-writer without having to be in the same room -- but I just can't figure out how to do it!

It seems I can send a sound file to email from my iPad's Garageband, but how would the singer import that file into their iPad's Garageband? Surely it can't be that difficult, but I've read a lot online and there just doesn't seem to be a way to do this.

Any suggestions or advice would be very gratefully received!