It turns out the T1 instability is a byproduct of either a bad cable pair, or a bad card somewhere along the line. The wonderful Engineers at our phone company don't know for sure. Either way, they're stopped the tests they've been running all day (this was the cause of most of the instability today) and don't plan on resuming them until their Engineering department can map out the line that we're on, which will be sometime mid-day tomorrow.
Again, once I know for sure that they've actually FIXED the problem, I'll post an update. For now, though, everything seems to be running smoothly.