Sending TV data over a normal dial-up telephone line is not a trivial task. I spent 6 years of my career between 1995 and 2000 designing and building video conferencing systems that did just that. You may be interested to know that there exist international standards for doing this type of thing so that video equipment from various manufactures can intercommunicate. Here is a summary:

H.320 Video Conferencing over ISDN phone lines.
H.323 Video Conferencing over a LAN / Intranet
H.324 Video Conferencing over POTS phone lines.

You can put any of the H.xxx numbers into a search engine like Google and get more information than you probably ever dreamed even existed on the subject.

It turns out that an 8051 derivative type part is not nearly up to the task of implementing something like H.324 all on its own. It will need the likes of a video compression chip (and if you do audio then also an audio compression processor) and a telephone line interface control mechanism. It should be possible for you to manage system control and call setup and teardown on one of the higher performance 8051 derivatives.

There is a company that you may want to investigate called 8x8. You can find them at www.8x8.com. They make an array of products that support video conferencing from the chip level to the software level and up to the system level. At one time they even made a low cost dial up unit that would have permitted you to do just what you are desiring to implement. Today I am not sure if 8x8 still makes the low end hardware anymore, but H.324 into Google will reveal plenty of companies that have their fingers into in one way or another.

Michael Karas