Agreed though - anything throwing unwanted noise onto the RF spectrum is a Bad Thing, however low-power it is (see powerline networking).
At the very most, we will see a migration of national (and possibly large regional) stations to DAB in the next decade. FM will still remain up and running for local commercial and community radio - and an expansion of this is planned once the spectrum currently used by national broadcasters is released. The current FM and MW spectrum is of little use for new technology like mobile broadband - they are more interested in the current TV spectrum and up into the GHz bands.
All this is currently under discussion, though, and nothing is confirmed. The status quo remains for now!
I've always been interested (just out of interest) to get an understanding of what the whole spectrum looks like, which bits are good (and why), and which bits are currently taken by what and could be used by other things.
Is there any good place I could find such a thing that you know of?
This rather psychedelic PDF is linked from the above page: http://www.roke.co.uk/resources/datasheets/uk-frequency-allo...
It doesn't say which allocations are good or bad - just what each slice of spectrum is used for. People like the mobile operators are only really interested in spectrum above the 800MHz area. This is where the competition for spectrum and billion-pound licence auctions come into play.
Cellular companies are interested in line-of-sight frequencies in the UHF and SHF bands, where range is smaller but robustness of coverage is high. Then, they just blanket their desired area with cellular towers. VHF travels further, at the expense of robustness - it's ideal for broadcasting, but not for two-way data services. If you cleared FM and transplanted the existing 3G service onto, say, 100MHz, you'd find all sorts of interference issues.
87.5-108MHz, for instance, is used for FM broadcasting all over the world (except Japan where it's down in the 70s). The receivers will be available for the foreseeable future - certainly for my lifetime. If the band was vacated and all radio migrated to digital, the pirates would simply use it. It is of such little value - so it may as well be kept, rather than switching to digital for its own sake.
http://www.bbc.co.uk/rd/pubs/spectrum/bbc-the-spectrum-and-i... (see page 5)
1] the carrier frequency doesn't itself determine the bandwidth, it's the frequency range that does. For example, if someone says "a 100 Mhz signal", that doesn't tell you what the bandwidth is. You need to also know that the signal is actually allowed to cover 99.9 Mhz to 100.1 Mhz, so it's bandwidth is 0.2 Mhz (which could transfer ~0.2Mbps (order of magnitude accurate), depending on the encoding system used[2]). But if someone says "a 100 Mhz signal" you can guess that they don't mean the signal is allowed to cover 70 Mhz to 130 Mhz (60 Mhz of bandwidth), because: a) that's a ~2x range in frequency, which make it hard to design appropriate aerials, filters, modulators, etc; b) that isn't how spectrum is actually allocated anywhere I know of. So in practice you can normally deduce the approximate bandwidth by knowing the carrier frequency. Apologies for the long explanation - I've been nitpicked before on this..
2] see: http://en.wikipedia.org/wiki/Nyquist_rate, http://en.wikipedia.org/wiki/Bit_rate
Anyway, the FM band is still in use, see the furore over iTrip or similar devices that were at a time banned in the UK as the law said you needed a license to broadcast on FM.
The FM band is still in use and even when radio goes digital AFAIK the idea is that the FM band would be available for alternative use once radio stations no longer require it.
Then, when Ofcom come calling, the FM transmission is "someone relaying our internet broadcast, we don't know who it is."