The only thing sent to my phone was three beeps. There was no voice or any other sounds. My assumption is that it's a telemarketing making up a list of cell phone numbers. I'm on the donotcall.gov list, which appears to have little significance in some circles.
The reason that it seems the Do Not Call List isn't working, is that telemarketers have systems that can robo call and create fake numbers and they get through the system with no problem, only to annoy the hard working tax payers. The Do Not Call List works, but it need to be updated to repel organizations that use more sophisticated methods.
Rang twice on my business cell phone and hung up. Have received two fake IRS calls on house phone in the last month from people with Indian or Asian type accents with threats to arrest for taxes which is ridiculous as they are fully paid every year.