Handful of pre-mango Windows Phone devices get tethering support

Though internet tethering is added to Windows Phone 7.5 (Mango), most using devices that were running Windows Phone 7 didn't get tethering capability even after updating their phones to Mango. The reason is that device manufacturers/carriers need to add new Wi-Fi drivers for these devices and they also have the option to provide or deny internet tethering.

The following devices are now getting updates that enable internet tethering.

• HTC Mozart (O2, One Call, Telenor)
• HTC HD7 (O2, T-Mobile)
• HTC Titan
• HTC Tropy
• Samsung Focus

If you are using any of these devices and  find OS update waiting to be installed, it's probably to enable internet tethering

Source