I don't think so. I think they actually fall in line behind several days of call-in requests. If you are trying to book something right at an 11-month or 7-month window, or otherwise making a booking where time is of the essence, I would strongly recommend calling MS.
When you call MS, you either have a confirmed ressie or you don't. You know immediately.
There is no actual Internet booking. What we have is simply an email request, which they will get to and fulfill when they can. If you are booking far in advance for a slow period, it may be okay. But I would certainly not use the email request for any important reservation. Lots of things can happen with that, and almost all of them are bad.