The Nokia repositories still exist and are essential for your phone's wellbeing. DO NOT disable them! The errors you see when running apt-get update and friends mean that the security certificates on those repositories have expired. We just have to live with that, no one is ever going to renew them.

In fact it is better not to remind Nokia/Microsoft about that; I suspect that the repositories are alive only because they forgot to switch them off. Before they do switch them off, better make yourself a backup like this:

http://talk.maemo.org/showthread.php...48#post1455848