Here is a link to the FBI announcement from May on Telephony Denial of Service (TDoS) attacks. I just noticed that they have a podcast on it.
Also, there was a post on the private member forum at the Communications Fraud Control Association (CFCA) about TDoS. Apparently customers are getting flooded with calls containing a recording in Spanish, references winning a contest. Here is a brief snipp from the forum post:
We have a customer that is getting blasted with calls from the following numbers: 586-992-8668, 541-844-2096, 734-217-9988, 702-224-2596. The calls are a recording in Spanish referencing winning a contest. The calls started on July 26, 2010 and terminate to our customer numbers 818-441-0100 and 818-815-3100.