CBS is taking the iPhone where no iPhone has gone before.

Today, it released an iPhone application for its TV.com site that can play full episodes of TV series, ranging from “C.S.I.” to the original “Star Trek.” While Hulu, a rival video site owned by NBC and Fox, has kept its content only for computers connected to the Web, CBS has been far more open with its own content.

All sorts of video have been on the iPhone from the beginning by way of its YouTube application and its ability to play podcasts (which now can be downloaded over a wireless connection). The application for the Joost service can play some episodes from CBS and other producers’ series. NBC tried a special Web site set up to stream episodes of a few of its series for the iPhone.

But the TV.com application appears to be the first with a lot of mainstream network content that can gain access to full episodes over both the cellular network and Wi-Fi. My test of watching Spock confront a strange cube-like object in space was perfectly acceptable in quality while I was riding on the bus in New Jersey.

As a commuter, I’ve seen a huge increase in the number of people watching video on various types of portable devices over the last year or two, particularly on their way home from work. So I wouldn’t be surprised if the TV.com service finds an audience, particularly if CBS can promote it widely.

I think this is an important and provocative development. Companies like Qualcomm have been developing special services for watching video on cellphones, like MediaFlo, using dedicated cellular bandwidth. If people can watch what they want using regular data services, it will make those extra fee services a much harder sell than they already are.

Of course, if streaming video becomes common, it may put pressure on the capacity of the wireless networks, forcing the carriers to consider how they price data service and whether they continue to offer unlimited bandwidth. But once people start using a service, it will be hard for carriers to cut it off.

Pressure will also be applied to NBC, Fox and ABC if the CBS programming becomes popular on the iPhone. As much as the networks are afraid of losing control of their distribution and cutting out their affiliate stations, they are equally afraid of falling behind rivals and losing potential audience.