It's worth noting that in the US carriers impact (or 'power' if you prefer) is much bigger than in the rest of the world. They may be resistant to Google's ambition, especially since Google has made it clear that they're interested in becoming a carrier themselves (http://mobile-thoughts.blogspot.com/2007/07/time-of-competition-peaceful-summer.html). And it seems to me that it really is a viable way without losing anything: if these carriers would like to enter mobile advertising market, they could make their own products for that purpose. For example, Google even helps them by offering their APIs for free. :)

If viewing advertisements could earn the user atleast some Cents - that would definitely attract some audience. I have came across a similar Indian website ( mginger.org ) , which pays you for reading SMS advertisements(never tried it myself though!).

Regards
Gopal