I just had HTC mail me this in relation to the new update issues with the 3G and Wifi which was just released on the 6th of Dec 2011;
Dear Alex Paps,
Thanks for contacting HTC.
We understand that after you updated your HTC 7 Mozart, the phone developed a MAC address issue and won’t connect to the network’s 3G service properly. Please allow us to address your concern.
To support WIFI hotspot on the concerned devices, the WIFI driver was upgraded and aligned with Mango (Windows Phone 7 version 7.5 update) projects. The API (application programming interface) to read WLAN (wireless local area network) MAC addresses is different, since the concerned devices uses SD memory, and Mango devices use eMMC (multi-media card). When there is a failure to read WLAN MAC addresses, a random MAC address is assigned so it can solve connection problems. This, however, causes similar issues to what you are experiencing.
We are aware of this issue with your phone and have already issued an update for your phone. This update will be available before end of 2012-January.
Please let us know if this information was able to help you with your concerns. If not, please advise us of the issues you’ve encountered.
Should you need further assistance, please feel free to share your preferred contact schedule with us as we would be more than happy to contact you directly over the phone for assistance. You may also give us a call at 1300-482-482. Our business hours are from 8:00am to 8:00pm Sydney Time, from Mondays to Sundays and closed on Public Holidays.