Google just now released (officially) device and carrier options, for targeting.
I can’t speak for other countries yet, but for the US we have:
For devices you can specify:
iPhone and iPod Touch (together)
Android (of course Google has that as an option!)
Palm and I would think as many people use Blackberry by itself.
For carriers you can specify:
What works for advertisers should be the many different spellings too. Changing the word a little may cause some more visitors to come to the site.
From my perspective it would be interesting to see how response varies between different devices and different carriers.
If nothing else some offers might work especially well for iPhone users – since demographically iPhone (and iPod) tends to be different. So some ads work better … and some ads work worse, for that audience.