Appears to be the solar energy telemarketers just using a different phone number with an unavailable caller ID. They just keep passing your phone number from one person to another. Doesn't matter if you are on the government do not call list. They change their phone number so often that they can't be tracked. You can block the number but they change it so often that it doesn't help. We just have to live with it.
Panasonic has a new model of cordless phone/answering system that lets you block entire area codes or area code + exchanges. It's the KX-TG572 unit, and it accepts up to 250 phone numbers *OR RANGES* to block.
In my case, a lot of slime display the 559 and 714 area code. I just blocked the whole damn area code! It's great.
This number 559 272-4586 - calls every day and stays on the line for a minute, then hangs up. They are a solar energy company and they are really pushy.