I'm just writing to inform whoever can help that I also have the same issue than Michael Meschenmoser since the OTA JB update: my Nexus S reboots randomly (not related to calls). Every one or two days I find the phone has rebooted when I want to use it. So between the time the phone reboots and I find out I'm unreachable.

I'm using an unrooted Nexus S in Belgium.

David