Well in the long run it becomes "who has the best implementation of MeeGo" instead, so the better question is what can they do to prevent themselves from becoming commoditized, which at least in the US only benefits the carriers.

The answer, of course, is branding of their devices, stores, and services. This is likely to be a bigger reason Android will face pressure from the handset vendors themselves (and hopefully the carriers too) as it essentially puts all of that in Google's court instead of their own. MeeGo (or indeed, any open source effort not wholly owned by one vendor) fills the platform niche nicely, putting Google out of the picture.

Now we just sit back and watch what happens, and hope that us end-users don't end up as collateral damage :/