I have unlocked my phone because I want to use it locally when I am in South America. I have a SIM for a local phone company. When I insert the SIM and try to use the phone in GSM mode a message says that there is no SIM installed and switches back to CDMA. Why? I bought a global phone from Verizon with this specific requirement in mind. I was persistent with the sales person explaining EXACTLY what I needed. That is the only reason I bought this phone. What is going on here?