I've just discovered that the Google Maps (US) click to call service (which was demoed by Steve Jobs during the iPhone launch) works with any US phone (I assume US numbers only - I'm not sure what would happen if you put in an international number). Even more interesting is that it's free to use - Google pay for the call between you and the business you are calling. All you have to do is enter in your phone number, and then Google calls you and then connects you to the business your calling.
Now if only this was available in the UK. And GTalk integration would be nice.