Voice-over-IP applications will be forbidden from Microsoft's Windows MarketPlace for Mobile store, along with programs that are larger than 10MB or that change the default browser on a device.
They are among 12 prohibited application types that Microsoft listed for developers who register to create software for the store. Marketplace for Mobile is due to launch in the second half of the year, along with Windows Mobile 6.5, the next version of Microsoft's mobile OS.
Wireless developers, whom phone makers are courting in the hope of attracting the best applications to their platforms, are closely watching the terms of new application stores, which also include one that has yet to launch from Palm.
While some may be unhappy about some of the restrictions, many will be pleased to at least have a clear set of rules. That contrasts with Apple's App Store for the iPhone, where it is sometimes unclear why applications have been rejected or approved.
Among the list of prohibited applications is VoIP services that run over an operator's network. That's a common item on such lists because operators fear that the services will displace their own voice offerings, which bring in the bulk of their revenue. Developers presumably will be able to offer VoIP applications that use Wi-Fi, though.
Also forbidden are programs that allow people to shop at competing application stores, or that change a phone's default browser, search client or media player. Developers will also be unable to build programs that change the default phone dialer, short message service or multimedia messaging service interface. That could help ensure that standards for services like MMS are upheld.
Microsoft recently began inviting developers to sign up to sell applications in the Marketplace. In launching an application store, Microsoft is catching up to Apple, Google and Research In Motion. Palm and Nokia are also developing application markets.
They will have to work hard if they want to catch up with Apple, which popularised the idea with its iPhone App Store. According to research from ComScore, 59 percent of iPhone users have downloaded apps. That's more than five times as many as the average mobile user and more than double Windows Mobile users, ComScore found.