A sportscaster had the opportunity to call a handful of games this basketball season on ESPN3. He is hopeful it will lead to a chance to broadcast games regularly for ESPN.
Do ESPN3 games lead to opportunities with ESPN? Maybe. This topic was recently explored in the STAA forums, with great insight provided by someone who has helped produce many E3 productions.
Your chances for moving up to ESPN partly depend on who hired you to do ESPN3 games.