A free app called YouCast for Blackberry should meet your needs. With this app, you can exchange media files with your blackberry friends instantly without worrying about file size limit. The push activation application is based on Wireless SMS or email. It works on WIFI and data plan, no PC required.

To install, point your bb browser to http://m.youcast.net/blackberry.html

Detail product information is at http://www.youcast.net/

Check it out!