I've come away a little confused on how to develop mobile apps for Ubuntu.

First of all, do developers need the Ubuntu operating system to develop for Ubuntu?

Is it possible to develop Ubuntu apps in Windows?

Also, PhoneGap was mentioned somewhere along the way. I'm guessing this is something which isn't implemented yet? Where can I find out more information?

I'm currently using PhoneGap to target Android and Windows Phone, so it would be great if I could target Ubuntu with PhoneGap too!