With so many different operating systems in the smartphone space, deciding where to launch a new app is no longer as simple as saying, ?iPhone.?

Sure, the iPhone dominates the market. But Android is quickly growing and there are circumstances when the much smaller BlackBerry or Windows phones might make sense. Developers are also keen on Windows? tools for developing.

?We?ve been witnessing the Web-to-mobile transition and the pace at which it is happening is staggering,? said Shehryar Khan, CEO of mobile software digital agency Ubermind, Seattle.  ?There is a lot of innovation coming out of the mobile space and a lot of interesting apps continue to be released.?

Choosing an OS
Developing apps for mobile phones is competitive, however.

?It is not that easy to build these apps and there are only a handful of companies that do it well,? Mr. Khan said.

One of the first questions most companies looking to build an app will ask is: ?Which is the best phone for reaching my target audience??

If sheer reach is the goal, then the iPhone wins, for now.

IOS has the largest installed base right now, per Mr. Khan. Android is a close second and is growing very quickly while BlackBerry and Windows still have relatively small installed bases.

However, the marketplace is quickly changing.

A recent report from Gartner predicts that Android will become the most popular smartphone operating system by the end of 2011, with its greatest opportunity lying in mid- to low-priced smartphones.

The report also suggests the Windows Phone will become the third largest platform by 2013 thanks, in large part, to Microsoft?s alliance with Nokia.

Apple?s iOS will remain the second biggest platform worldwide through 2014 as the company maintains its premium pricing strategy.

Research In Motion?s share of the market will decline.

Going for aesthetics?
Besides the iPhone?s large customer base, developers also often turn to it for its cache.

?If the desired app is not only a functional application but also a statement of technical edginess, then we have to get an iPhone app done first and foremost,? said Patrick Emmons, director of professional services at Adage Technologies, Chicago.

However, if a company wants to reach a specific audience such as healthcare workers, lawyers or those in the financial services, then BlackBerry or Windows, which have strong penetration into these markets, may be the right decision, per Scott Michaels, vice president of app development firm Atimi Software, Vancouver, Canada.

Sometimes it is not about reach, however.

?If the customer is more focused on reduced cost of platform development, then we can start with the Android platform,? Mr. Emmons said.

In fact, several industry experts interviewed here pointed to the growing trend of developing apps for the Android at least in tandem with the iPhone and sometimes prior to it. The development tools and end-user experience is considered a close second to these for iOS.

There have been some problems around ActiveSync due to unique implementations of the open-source Android platform. However, these are likely to be ironed out soon, per Mr. Emmons.

When it comes to the actual development process, there is not a consensus over the superiority of iOS, with some insisting Android has the best development tools, database access and multitouch capability.

Others, however, point to Apple?s emphasis on speed and reduced battery consumption, which means working without the bells and whistles of java or .net.

?It?s difficult to develop a corporate app [for iOS] that leverages external xml-based data repositories due to its lack of xml parsing,? Mr. Emmons said. ?It will take longer to write an app for iPhone than it will for Android or Windows.?

BlackBerry vs. Windows
When it comes to the BlackBerry, developers mostly agree that the environment is not optimal.

?BlackBerry was already in full-on decline,? Mr. Emmons said. ?Its development tool and its user experience were not keeping up for a while. The Playbook was the final submission of defeat.?

Windows, however, is considered an up-and-comer. It offers developers a strong set of tools, including lots of tools for building mobile Web sites, per Ubermind?s Mr. Khan.

And, with the merger of Nokia, Microsoft has an opportunity to take a stronger stance on the actual device.

?If Microsoft can leverage its merger with Nokia to improve the quality over Android while still providing more than one phone option, then Microsoft might become a bigger player,? Mr. Emmons said.

One trend that several sources pointed to is the growing use of HTML5 for portions of an app that can then be easily leveraged across platforms.

?Most shops use a lot of HTML5 inside apps,? Atimi Software?s Mr. Michaels said. ?That Web piece is most easily translatable between iOS, Android and somewhat to Windows but not so much RIMs.?

In the end, developing a successful app for mobile phones is all about keeping up with what consumers are expecting in a mobile experience.

?The overall expectation of the level of quality has been raised for apps,? Mr. Michaels said. ?Today, you could never get away with some of the early apps that came out.

?People have now spent hundreds of thousands of dollars developing apps and if you?re not going to compete at that level, you?re chances of success are so much lower,? he said.

Final Take