According to Tom Brühwiler, Swisscom will release the Android 2.2 update for the HTC Desire next monday, August 23rd 2010. So at that point, you should get a notification on your device, that an update is ready. Please make sure, you are connected to Wifi as the update is over 90 MB in size. And make sure you have at least 25 MB of space left on your device and SD card.
Took Swisscom long enough. And their communication with customers is bad, really bad. I have asked over two weeks ago about a status on the update and didn’t even get a single line or comment. On the other hand, Sunrise responded within 1 business day, telling me they have already pushed out the update to their customers.