Using mobile parts?

Usually I'd be all for ripping stuff apart to get bits, but I'm afraid DrAzzy is right (at least as far as newer phones are concerned). Even if the bits could be interfaced to Espruino, often the connections are so small it's almost impossible to connect to them - It's best to stick the S3 on eBay and use the money to buy some components on breakout boards :)

Having said that...

• On older candybar phones, you might be able to use the LCD display - however it's probably a lot easier to buy a board with the LCD already attached as it's only a few pounds - for instance: http://www.espruino.com/PCD8544
  
• You can actually use some old Nokia/Sony Ericsson phones (again, probably the candybar ones) as-is, and can then send/receive text messages via Espruino.
  
• Lithium batteries from pretty much all phones are awesome for Espruino. A lot of the batteries have simple flat copper connectors on them, which you can easily solder wires onto. The S3 battery is around 2000mAh, which can power Espruino for over a year (if the battery doesn't self-discharge first!). A bit more info on that is here: http://www.espruino.com/Battery
  
• Phone chargers are generally pretty good at powering Espruino too.