Stephen Hawking is a forward thinking fellow, so when he was told his synthesized voice sounds a bit outdated he decided to call up some of his famous friends and let them have a go at becoming his new voice.
Okay, so the whole thing is just a funny bit by Comic Relief, but if Stephen ever does decide to get a new voice for his speech synthesizer he's got quite a few great voices to choose from!
-Via Geeks Are Sexy