Every mobile operating system now has their own on device application store, thanks to the initiative of Apple with the iPhone and the App Store. You can buy apps through all of them on your phone, but not all of them support buying apps from your desktop PC. According to WM Experts Microsoft just kicked off phase II of the Windows Marketplace for Mobile by providing the capability to browse and purchase apps from your web browser. Simple visit http://marketplace.windowsphone.com from your browser to check out the store.
You can still only officially get to the Marketplace on a Windows Mobile 6.5 device, but there is a CAB file available so you can put the store on your 6.0 or 6.1 device and it works just fine on my T-Mobile Touch Pro2.
You use your Windows Live ID to sign into the online store and you should see your purchase history made from your device. You need to have a device registered with the store before you can buy apps. You register your device by signing into the Marketplace from your Windows Phone and once that is done you will see the Buy button activated online. I tried to make a purchase, but the card associated with my Windows Live account is old and the system wouldn't recognize my new card so I will have to wait for everything to work through the system before I can test out this new capability.
I was thinking this web access would download the file locally and then require you to ActiveSync to get it on your phone, but Microsoft makes the process much easier by sending you a notification (via text) that an application is ready to download. You follow the link and download right to your phone. There is no mechanism to backup and save purchased apps on your PC so like the other mobile application stores you have to rely on the company to provide access to your account and purchased apps if needed. Microsoft clearly states you will be able to reinstall by signing into your account on your phone so redownloads are not an issue like they were with the Nokia Ovi store.
As a mobile enthusiast, I was also pleased to see Microsoft has a policy similar to Apple where you can have up to 5 phones associated with your Windows Live ID account. As long as the apps you purchased are compatible with your new phone, you’ll be able to download and install them from the My Applications page on the new phone.