Incoming calls have been doing this on several of my phone numbers today. They work for awhile, then don't work. Typically inbound callers tell me they call won't ring through, rings busy after and extended period of time, or connects and then disconnects. For me, it will ring through, but when I answer it silent, then I get a fast busy after about 5 seconds.

I've submitted a ticket on this, but this does seem to be a common problem that's getting worse.