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I have had FIOS service since October 9, 2008. Until two weeks ago, I was constantly getting the "Currently Unavailable" message and rebooting about every other day. Then, it stopped. It has been working perfectly for the last two weeks. I have been delighted with the service since this issue has stopped - hopefully for good. I still hate the IMG for its lack of accuracy and information.
As a side note, my billings have been perfect.
Interesting comments, but the reality is that FiOS worked fine for several days after it was first set up on this set (Magnavox HDTV) before the "Channel Unavailable" message started on all channels.