How many app stores are too many?

Encouraged — or perhaps terrified — by the success of the recently launched iPhone App Store, every device-maker, software provider, mobile operator and their brother seem ready to launch a competitive offering.

Announced or rumored app stores from Google, Microsoft, Nokia and others come as operators ramp up creation of their own off-deck, more “open” applications.

The challenge for operators is whether consumers will prefer to get apps from companies known for delivering them — essentially, software companies — especially after carrier decks have received criticism for their lackluster approach to innovation and new services.

The iPhone App Store, which runs on the phone itself and also is accessible on the desktop via Apple's iTunes program, had delivered more than 100 million applications by mid-September — a little more than two months after its launch. Developers report vastly better results than previous distribution channels, including independent app stores such as Handango or selling directly via the Web. Photo-sharing app SmugMug said its iPhone new account registrations are “300% better than all our other registration avenues combined,” said SmugMug co-founder Chris MacAskill.

Not to be outdone, Google recently announced Android Market, which Eric Chu of Google's mobile platform project described as an “open content distribution system,” meaning that developers can upload, host and distribute apps with little to no interference from Google. Like the iPhone App Store, Android Market will run on Android phones, making it easy for users to download new apps.

New launches don't stop there. Microsoft is reportedly going to launch its own app store sometime next year, dubbed SkyMarket, to support Windows Mobile 7. T-Mobile is also rumored to be considering an app store launch — perhaps in conjunction with Android — while Nokia, RIM and Symbian all look ready to jump on board as well.

But will applications, and app stores, sell phones? The iPhone seems to say yes, but in the end, said industry analyst Avi Greengart, “Consumers don't buy [applications or operating systems]; they buy devices.”