Not really. I usually keep monitor running (and logging to a text file) so I can trace that kind of stuff. Lack of a background kills in this type of troubleshooting. What kind of phones? If 44xx, did their "message lights" flash (happens on boot up). On 64xx and 54xx/24xx the names disappear for a while on the display until the system is back up.
We know it rebooted, but the cause is what we can't figure out w/o having trace from that moment. I'd see if you can arrange to have your VM Server keep MONITOR running all the time, then if this happens again we can look at exactly what happened on the IPO to cause the reboot.
I will say this, 3.0 had issues with phones sometimes not coming up after soft-reboots and I see you have 2 PRIs (which was part of the issue). 3.1 is much better, but the problem still exists. I would recommend upgrading the system to 3.1.48-PB4501. Its a private build based on 3.1.48 that corrects an issue with rebooting when CDR is active (a new feature of 3.1) and someone from a conference call hangs up. If you have no need for the CDR feature, 3.1.48 or 3.1.56 would be fine. If you do have a desire for CDR, use the 3.1.48-PB4501 because 3.1.56 does not have the fix in it for CDR yet.
BTW, since you do have 2 PRIs, make sure only one of them is set for Clock Quality=Network. The other should be set to Fallback. This can cause issues.
Hope this helps...
Kris G.