Mobile operators that joined Google for the launch of the Android mobile platform see a vast army of developers lining up on their side to help get new applications out to eager subscribers.

The open-source, Linux-based platform, expected to start appearing on devices next year, includes an operating system and a full Web browser. A free SDK (software development kit) for it is due to come out next week. There's nothing in Android to keep carriers from developing a locked-down phone with just a few available applications, although it's unlikely because the more locked a phone is, the less it would take advantage of the platform, said Google Chairman and CEO Eric Schmidt.

Most mobile phones today run either proprietary operating systems or one of a handful of platforms such as Research in Motion's BlackBerry, Microsoft's Windows Mobile and Symbian. Mobile operators, especially in the US, currently dominate the choice of phones and applications. The two major carriers that signed on with Google Monday, T-Mobile and Sprint Nextel, are the underdogs in the US market and may be looking for a way to shake things up, said analyst Albert Lin of American Technology Research. T-Mobile USA said an open platform is needed to deliver what customers want.

"We're not going to be able to come up with enough stuff that we're going to be able to make up in our own shop," said Joe Sims, vice president of new business at T-Mobile USA. Because it is open source, Android will make it easier for third-party developers to bring their applications to different phones and carriers, he said. He expects a wave of innovation similar to the Internet's, spawning a variety of new business models. For its part, on Android-based phones, T-Mobile would approve applications and allow any as long as it didn't harm the carrier's network, cause a bad user experience or harm T-Mobile's own business, he said.

Sprint wouldn't even place those restrictions. In some cases, the carrier might allow users to download and install new applications without Sprint even knowing about it, spokesman Scott Sloat said.

Android could make it easier for separate parts of a phone's software to communicate, said Kevin Packingham, vice president for product development with Sprint. For example, a social-networking application could use an Android phone's address book, calendar and location information to help consumers arrange to meet each other, he said. For businesses, it could make it easier to port enterprise applications to various phones, he added. Today some developers do the same thing with Java, but the many implementations of it make that difficult, he said.

Easier development could make it feasible to bring "long tail" applications used by a relatively small group of users to phones, Packingham said.

Verizon Wireless and AT&T's mobile division both said they support giving consumers many choices, but they didn't sign on with Google's newly formed Open Handset Alliance on Monday. Verizon has been in discussions with Google and might yet join, spokesman Jeffrey Nelson said. Either way, he expects an impact.

"Just as the introduction of the iPhone has focused mobile consumers on the music offerings of all service providers, I think the focus here on a new OS and on open development will also spur innovation beyond its own walls," Nelson said.

The large incumbent carriers partly are cautious about maintaining their own revenue streams, analyst Lin said. When subscribers pay for mobile applications or content today and are charged on their carrier bills, nearly half of the fee goes to the carriers, he said.

"If the carriers didn't demand that kind of direct payment for use of their network, it would open the business model for greater capability," Lin said. For example, it could open the door to more ad-supported services or applications, he said. Consumers ultimately will demand the more open model Google promotes, and Verizon and AT&T know this, he said.

Still, none of the carriers or other parties in the alliance has made a commitment to using Android, and adoption will take time, analysts said.

"It would take a long time for this to have any impact on consumers," said analyst Jason Kowal of Analysys. For one thing, although the software may be free, the time involved in getting it on a handset is not, he said.