Comcast and Charter — the No. 1 and 2 cable operators — have just confirmed their alliance, disclosed last night, to jointly “explore potential opportunities for operational cooperation in their respective wireless businesses to accelerate and enhance each company’s ability to participate in the national wireless marketplace.”

They say, in a release, that they want to see whether they can agree on what they describe as “a common operating platforms; technical standards development and harmonization; device forward and reverse logistics; and emerging wireless technology platforms.”

Just as important, they’ve agreed to “work only together with respect to national mobile network operators” for one year. They specify, in an SEC filing, that during that period they can’t make a major deal affecting their wireless businesses without each other’s “prior consent.”

Indeed, if Comcast or Charter has “any contact directly or indirectly with a third party” then either must “”promptly inform” the other and keep it informed in all material respects of any such discussions.”

That would appear to at least temporarily preclude a the much speculated upon idea that Charter might sell itself to Verizon, or make a run at T-Mobile or Sprint.

Charter shares are down 4.4% in pre-market trading.

Comcast and Charter have announced that they plan to offer wireless services that would heavily depend on their wifi networks, with cell calls handled by Verizon as part of a deal it made with leading cable companies several years ago.

Comcast plans to launch its Xfinity Mobile service before the end of June. It would be available to customers in its existing markets to supplement its video, internet, or wired voice products.

A similar offering from Charter is due in 2018.

The new alliance will enable them to “explore ways we can make our respective wireless initiatives more efficient and cost effective,” Comcast CEO Brian Roberts says. “Both of our companies have regional wireless businesses using the same 4G LTE network, and by working together our goal is to create even better experiences for our customers.”

Charter CEO Tom Rutledge says that the alliance with Comcast will “not only speed Charter’s entry into the marketplace, it will also enable us to provide more competition and drive costs down for consumers at a similar national scale as current wireless operators.”