Quick post. In light of recent Nokia+Microsoft-MeeGo news, I have gone to learn more about Android in a hurry. And here is the first result - MorzeSMS.
Basically it is a tiny app that will play a morze code when you receive an SMS message. The morze code is the phone number of the sender in 'cut number' morze form (to be shorter). The idea is that first of all morze is a cool sound and second is that each sender gets a unique sound that you can learn to identify over time so that you know who sent you a message as soon as you hear the beep.
This is very early beta - there is no UI, no configuration. You can download it here. Leave bug reports in the comments of this blog post. It does not disable the stock SMS-received sound.