Microsoft will close access to its Marketplace for all devices that haven’t been updated to Windows Phone 7.5 Mango In the coming weeks. Users would only be able to browse the Marketplace if they haven’t updated, but they won’t be able to install apps.
Microsoft explains the requirement for Mango as follows:
“Requiring Windows Phone 7.5 is part of a larger effort aimed at improving Marketplace performance and security, and paving the way for even faster growth and more new features.”
All WP devices released so far can be updated to Mango, the user need to connect his WP smartphone to a computer with Zune, let the process go for around an hour after following Microsoft’s instructions all along. You can find it in this link.