Taking a page from the Internet, the mobile communications industry is moving toward a more open approach to cell phone applications. From Apple’s App Store, to Microsoft’s Windows Mobile and Google’s Android, these platforms are changing the way the software development business gets applications on consumer phones.

For years carriers have prevented the installation of third-party software over concerns it would hurt the network, erode user privacy and negatively impact the user experience. But as cell phone technology advances and the popularity of using the Internet via phone grows, the old way of doing business is changing.

“Carriers are realizing that that’s wrong for consumers so we’re seeing more operators go towards the unlocked approach,” said Scott Rockfeld, group product manager at Microsoft’s (MSFT) Window Mobile.

In the last two years telecommunications carriers Verizon (VZ) and AT&T (T) have announced they’re moving to a more open approach with applications and devices. “Our customers are able to download virtually any application to their handset without restriction,” said Heather Buffington, a spokeswoman for AT&T.

The movement toward a more open platform has ushered in a handful of services to let developers make applications for mobile phones. And developers are responding in droves.

Take Apple’s (AAPL) App store which was launched on July 11, when Apple’s latest version of the iPhone came out. The  store lets iPhone users download more than 900 developer-created applications directly to their phones. Natalie Kerris, a spokeswoman at Apple, said since the launch less than a month ago over 25 million applications have already been downloaded.

One of the most popular paid apps at the moment, according to iTunes, is Crash Bandicoot Nitro Cart 3D, a racing game by Vivendi Games Mobile. The game, which costs $9.99, is controlled by tilting the iPhone to turn the vehicle you're racing.

Another app, CityTransit NYC Subway Guide by Magnetism Studios, provides a New York City subway map and uses the iPhone's GPS locator to find the nearest subway station. This program costs $2.99  AOL's  instant messenger program is among the top 20 free apps

"The App Store has been a catalyst for the whole industry in general to move to a broader set of applications and try to encourage developers to come forward and develop these apps by lowering the hurdles to get these apps to market,” said Matt Murphy, partner at Kleiner Perkins Caufield & Byers and manager of KPCB’s iFund, which is a joint deal with Apple to invest in companies that make applications for the iPhone and iPod Touch.

Apple’s App store is located on the iPhone, which Murphy said makes it easier for consumers to find. And since the applications only work with the iPhone, developers don’t have to contend with creating the same software for all types of phones.

One problem that’s been an issue for almost all platforms is compatibility with multiple handsets, said Ross Rubin, director of industry analysis at market research firm NPD. “When you develop an application for one phone, there are many minor variations that interfere with that application running so it needs to be tweaked for a number of phones, even if they’re with the same manufacturer,” he said.

Verizon, for its part, lets subscribers buy applications through a system called Brew, but Verizon gets to choose what applications are on Brew, said Rubin. With a new Open Development Initiative, manufactures will soon be able to make devices with any software that after some basic certification can have support for Verizon’s network built-in, he said. That means handset manufacturers will be able to put any software they want on the devices without Verizon having a say.

“Our Open Development program is currently focused on new devices and the software that runs (or will run) on those devices, rather than on software that would be ‘ala carte,’" said Verizon Spokesman Jeffrey Nelson.

Microsoft, with its Windows Mobile operating system doesn’t restrict developers to the device or a Microsoft-controlled portal. Rockfeld at Microsoft’s Windows Mobile unit said applications can be distributed through third party Web sites. Rockfeld said there are roughly 18,000 applications that work on Windows Mobile.

Google takes a similar position with Android, letting the developers choose how to distribute the applications. Android isn’t available on phones yet, but devices powered by Android are expected to come out next quarter.

“We’re not interested in telling developers that we know best how to distribute and market their applications,” said Dan Morrill, Android developer advocate at Google.

Google’s Android is open-source, which Morrill said makes it customizable from the device to the application. For example Android could enable a developer to create a custom home screen for older people who may be intimidated by cell phones. The current market would make that difficult because the home screen might be locked down, he said.