Dargens works on the train.
As I write this I am downloading MP3s while on the 7:30am Waterloo to Portsmouth Harbour train.
As Dargens is a friend to Friend peer to peer service it keeps its connections and downloading speed despite the intermittent nature of internet connection while on the go.
Just need to sort out battery life now.
I have start working on a version of Dargens for Nokia N95 if anyone is interested.