It's called 'caller id spoofing'. The people calling you can make any phone number show up on your caller id. They're making a number show up that charges you money if you call it and press a certain key.
At the same time they've disguised the messages on their pay by phone system as surveys. Those messages normally tell you what you're buying and how much it costs.
Check your bill for unwanted charges if you called this number back.
Just got a call also on my cell. Didn't answer/no message. I can't beleive I found this site! I keep getting more and more of these calls on my cell and it's really annoying.