Just as Apple as done for its App Store, Microsoft has outlined some criteria that will prevent an app from being listed at the Windows Mobile Marketplace. Unlike the iPhone though, I don't think these apps can be banned from the platform, they just won't be at Microsoft's application store.Apple can not only ban apps from the app store, effectively banning them from the platform, they can also remove them once installed as they did with some tethering applications a few months ago. Unless Microsoft has some big changes not yet announced, you should still be able to download and install these apps directly unless your carrier or company has locked down the phone. If the carrier does it, that is a good reason to jump carriers. If your company does it, well, it is their phone, right?

So, what isn't allowed? First of all, apps that modify the carrier provided phone dialer, SMS app or MMS app. In general, MS provides the dialer though carriers can customize it or use their own. I suppose a carrier could modify the SMS app, though I've never seen one do it, so this is MS's app. MS doesn't provide an MMS app, so you get whatever the carrier provides, which is usually a substandard app compared to the Inbox/SMS app MS provides.

Speaking of changing apps, anything that changes the default media player, browser or search client is out as well. That doesn't necessarily mean you can't download another media player such as CorePlayer, a fantastic app that supports Youtube and way more codecs than Windows Media Player does. It just means that if CorePlayer can take over the default settings, it will be blocked. I would hope other browsers would be allowed too, though with the new IE6 based browser of Windows Mobile 6.5, another browser might not be as necessary. Recall, WinMo 6.1 and earlier aren't supported by the app store, so MS isn't trying to protect Pocket IE's turf here.

VOIP apps are out, at least for those that use the carrier's data connection. It is unknown if apps that are strictly WiFi based will be allowed. I am not sure how that is really possible though. While an app technically can distinguish between WiFi and cellular data, they really just look for a network connection and use it. That means Skype is out, though you should be able to download and directly install it. It does make me wonder if Skype will come out with a chat only client with no VOIP capabilities for Windows Mobile.

There are other prohibitions that protect the consumer, such as apps that publish the users location or share the user's information with anyone without the users express permission via opt-in. Once the user has opted in, they must have the ability to opt-out at any time.

The full scoop on banned apps can be found in this document.