Champions of a more open Internet could take a small bit of cheer from Yahoo’s plans, unveiled today, to open up its mobile platform to third-party developers. But the lack of a service-provider partner to endorse the idea is one clear sign that chief Yahoo Jerry Yang and all the other exclamation-pointers have a long way to go before they can expect to have a major impact on the growing market of the mobile web.

To be sure, plans like Yahoo’s Go or Google’s Android, which aim to bring the power of the open Internet to your handheld device, seem a preferable future than locked-in services like Verizon’s VCast. But without a service-provider partner to watch its back, Yahoo (YHOO) seems unable to answer a big looming question for open-Internet apps accessed via a cellular phone: How fast will the app perform, and how much will it cost to download the data?

Here at CES this year, there’s evidence of a trend toward more single-purpose devices or agreements (like Sony’s Skype/PSP deal, which has BT as the phone power behind it) that are complete with the service necessary to deliver the goods.

On the video side, LG has an interesting plan to give existing broadcasters a mobile outlet, just another one of the competing methods arising to bring TV to places you never thought possible. But like Yahoo’s ideas, such plans don’t mean a whole lot unless the service providers play along.

Since we weren’t able to view the Yang speech live here at CES (long bus lines and the absence of transporter technology kept us from getting from the Sands to the LVCC in time), we weren’t able to question Yahoo folks afterwards about service-provider buy-in for Go 3.0. But there’s plenty of time ahead for answers.

Paul Kapustka, former managing editor for GigaOM, now has his own blog at Sidecut Reports.