You're basically making my points for me now.

Regarding co-branding, nobody needs to make an iPhone-AT&T association for it to be an example of co-branding. People buy iPhones based on the shiny Apple ads, which sells AT&T service plans. Apple and AT&T both have giant ad budgets, but Apple is famous for running good ad campaigns, and since the phone is the thing moving cell contracts and not vice versa, it makes sense for Apple to do the heavy lifting on the advertising front.

On the Palm/Sprint side, things are a lot different. Both are battered companies looking to make a comeback. Palm has the hot phone now, and it has definite advantages over the competition. Neither is known for great advertising. Why does Palm have to be the one to run the ads, and why do the ads have to focus only on the positive for them to be effective?