I got 4 calls from this number... Same crap.  I answer, they hang up.  Called back, and recorded msg says "Avanti USA".  

They're now blocked from my call list (Thanks, T-Mobile).  

A note to you who may get calls from "collection agencies";  You did NOT go into ANY contract to do business with these scum - they may have "bought" your debt-ed account from someone you DID go into contract with, but not them. Therefore, you may OR MAY NOT CHOOSE to do business with them.  

I'm no lawyer, but I know my rights (at least where I reside). I ask them to send me a copy of my signed agreement to do business with their company.  As they cannot, the calls stop for me.