HTC seems to be on Android 2.2 release spree across Asia. India is the third country to get Android 2.2 update on HTC Desire after Singapore and Hong Kong.
As it is an over-the-air update, your HTC Desire will receive a notification of FOTA update when it is made available. Simply press OK to accept the update via a data connection such as Wi-Fi or GPRS/3G.
Instructions from HTC:
After installing the update, you can confirm a successful update by confirming the Build number (From the Home Screen go to MENU> Settings> About Phone> Software Information> Build number). The new Build number after the update will be 2.13.720.1. Update: Android 2.2 and HTC Sense update. Note?Please back up your data first before upgrading your phone. We recommend using a free Wi-Fi hotspot or an unlimited data plan to apply this update.
Do not panic, if it takes time for Android 2.2 update to reach your phone, as the update is rolled in batches.
Do share your experiences with us.
Via HTC Support