Yesterday night, Microsoft and HTC have released Windows Phone 7.5 updates for their Mango OS and devices. While Microsoft's "7.10.7740" release is a general update for all Windows Phones (even the brand new Nokia Lumia 800 has received it and this phone was only launched this week), the "HTC Update for Windows Phone" adds the missing WiFi tethering functionality to the company's first generation Windows Phone 7s. Other than that, the Microsoft update is a bugfix only which fixes an issue related to Microsoft Exchange 2003. With this fix, original messages are now included if the E-Mail is replied or forwarded. Another fix corrects voicemail notification issues.
If you haven't received the update message on your Windows Phone yet, connect it to your Zune Player to get the update notification.
Cheers ~ Arne