[neilwillgettoit]

It's just a low power FM station with a raspberry pi in it as a controller. It would be highly illegal to use this device in most modern nations without a license.

[voltagex_]

The Nokia N900 could broadcast short-range FM with RDS, I'm not sure what advantages this has.

[neilwillgettoit]

higher power. The n900's transmitter was 15nW (1.5e-8 W), which is why it was legal. For a claimed 6km radius, I would assume this is about 3-7W output.

[zumatic]

A 6km radius would fit quite well with schemes like Community Radio in the UK:

http://consumers.ofcom.org.uk/tv-radio/radio/a-guide-to-comm...

...still need a licence, of course.