Did some research on this and it may be a number used by the Corrections Corporation of America's Eloy Detention Center in Arizona. This is a facility used by the Department of Immigration and Customs Enforcement (ICE) to house male, minimum security immigration detainees. This facility also houses the Eloy Immigration Court. If you know someone that may have been picked up by US Immigration Enforcement personnel and they are being detained in a facility like the one in Eloy, Arizona they may have access to pay phones from which they may make Collect Calls Only. These phones are not well maintained but they are monitored. Since inmates may only make collect calls from these phones you will be asked to accept the charges for calls made to you from these phones. However, you should know that "collect calls" do not go through if made to a cell phone number. Cell phone customers are not allowed to receive "collect calls" from pay phones or any other type of phone. Cell phone companies do not allow their customers to receive, much less accept calls of this type so the moment that it detects that a call is this type of call you will be disconnected. So, those "hang-ups" may just be that your cell phone carrier has disconnected you once it determines that the call is "collect."
I hope that this helps!
here is the link to CCA's Eloy facility page: http://www.correctionscorp.com/facility/31/