At about 5:15 AM this morning our oldest dialup server suffered a power supply failure. This caused 48 incoming lines to go offline. At about 5:45 AM the 48 lines had been moved to two other access servers and full capacity was restored. Because this happened off peak hours it didn't appear to have affected too many people as there are generally only a few on at this hour.
Upon inspection is appears that the power supply may have been failing for some time. Either prior to the failure or at the time of the failure it appears that some of the voltage regulation on the main board itself also failed. I may have just found the cause for the random disconnects that have been reported over the past month.
At this time all services have been restored.