NVidia has published a white paper on the benefits of multi-core processors for mobile phones. This is one of the easiest and insightful whitepapers. I would suggest to go through the whitepaper to understand how things work...! Worth your time..
And by the way, NVidia is already working on a quad-core processor for mobile phones :)
To quote Jen-sun Hang, CEO of Nvidia "Dual-core processors will be the standard in 2011, and quad-core is coming in the near future!" Hail Super phones :)