The issue with mobile phones are that each and every mobile plays different video types.

Currently the only video format that nearly all mobile phones will play is 3gp.

What would have to be done is whilst the videos are being converted to flv they also get converted to 3gp within a different folder etc..:

flvvideo - flv files
3pgvideo - 3gp files

Each file would have the same number etc:

1.flv = 1.3gp
2.flv = 2.3gp
and so on...

From here it wouldn't be to hard to develop a system where users can download the 3gp file within the main site. Turn on pack features and this way you would get paid for the sites usage.

Hope this helps.
Regards,
Mat.