It's a scam. It's getting more and more widespread.
The way it works is, you receive a call from a number you don't recognize, then when you pick up they hang up, or you might here somebody before hanging up. Other times they let it ring a couple of times and hang up.
The whole point of the scam is to get you to call them back, at which point a charge is placed on your phone.
Sometimes is just a few cents, other times it could be quite more. So the simple thing to do is to ignore the call, and add them to your block or ignore list if your phone allows you to do that. My S3 allows me to add the number to a "Reject List"
Got a call at 11:38am. Didn't answer and no voicemail left. I called back and it said "the person at extension 900 is on the phone, please leave a message. " I hung up and blocked the number
Got a call from this number about 20 minutes ago. Didn't leave a message. My new Panasonic will block any calls. So just added it to the block list. So far I have four or five numbers that called daily, on the list. Thankfully, it's working like a charm. Not only does it block the call, but you can check back on the caller ID and see who it was that got blocked.
Female called saying she is from a cash company. Told her she had wrong number and hung up. Called the number back voice automated system says I reach voice box 900 leave a message after the tone. This is some type of scam.
I have received several calls on my cell the last couple days all times of day and night. Never leaves a message. I reverse dialed and got a recording "the person at extention 900 is on the phone". ...lol.. .really because I did the reverse dial at 3 am..!! Gotta be some sort of scam..