Just an FYI, I spoke with a Nokia Customer Service rep about the WP8.1 warranty issue yesterday. I'm in the middle of trying to get my 1520 repaired due to a software issue (I think). She informed me that my warranty was, in fact, no longer valid due to my participation in the dev preview program and the fact that WP8.1 was installed on my phone. Here is her email:
"Hi Matthew,
Thank you for emailing the Nokia Careline.
We understand your frustration regarding your phone. In response to this, please be advised that the reason why your phone's warranty expired is because of Windows 8.1 developers preview. The Windows 8.1 developers preview is not yet official and as said in the terms and condition for installing the said software it voids the warranty of the phone. And we cannot replicate this as there is no official Windows 8.1 released yet, the only place where you can get support is from Microsoft Developer Network forum:
http://social.msdn.microsoft.com/Forums/en-US/home?forum=winphoneosissues
http://dev.windowsphone.com/en-us/develop/devpreview
We are hoping for your understanding and we appreciate your patience and cooperation regarding this matter.
If you have any additional questions, please do not hesitate to contact us again. To ensure proper handling of your case, kindly continue using the current subject line.
You may also call Nokia Careline at 1-888-665-4228 from Mondays to Fridays at 10:00 a.m. - 8:00 p.m. EST (closed on national public holidays) for immediate assistance.
Kind regards,
Jacqueline M.
E-mail Specialist
Nokia Inc."
I don't buy her excuse, but it is what it is.