Its a long and complex answer and i am not sureit will be easy but basically you need to:-

Capture the video
Compress and encode it to the moving pictures expert group standard
tramsmit it through a gsm modem to any given network

any one of these would be a major project in itself.
Good luck

you are probably going to wish you had choosen a 16 bit processor about the time you start to look at whats required to encode the video on the fly.

Thinking about it I would seriously recommend that you dont even attempt this with an 8 bit processor.