Low-cost, high-impact technology: $5 cell phones?

Let's see whether we get beyond the press release from Philips (via NextBillion), who promise a:

...sub-$5 system solution – an integrated hardware and software platform constituting all the electronics needed in a mobile phone – that will drive handset costs below $20... Currently, the lowest cost mobile phones on the market are just below $40.

This would obviously increase demand. From The Economist:

Azmi Mikati of Investcom, which runs networks in Africa and the Middle East, estimates that the number of users would double in those markets if the cheapest handset cost $30 instead of $60.

Then the $10 phone and the $5 phone... The Wall Street Journal discusses all the contenders. Unfortunately, as Pablo has mentioned, connection taxes can easily be $15.