I'm trying to find software that lets you send a video clip from a website to a cell phone, and charge for this service. I'm wondering what backend system would be needed for this, to connect to mobile networks in different countries for example.

Im not so sure that is the way to go....

With file sizes now nothing is sent via mms anymore - it is all done via mobile internet. You may also want to try looking at E-mail technologies.

I cant help with regards to software however, I'm guessing some sort of server would be required to send files wirelessly.

Very complicated by the sounds of it! Good luck though.

yeah , how about searching for a software that lets users create a profile which provides a wap page and upload options . SO that user can upload his video or select from Site`s list and download via mobile

You can try!

Good luck