The 209 area code is for the Central Valley in California. That doesn't mean the call is good or even the real number. The IRS does have a huge processing center there in Fresno but they would leave a message with a toll free call back number AND a case number. With the hang ups mentioned in this thread it is probably not them.
You are probably correct about initial contact, but they DID call me. They claimed a letter was mailed within the last month. I looked up the IRS and called and the message and case number were for me. They use toll free numbers to call.