I have had a Samsung Intrepid (which has a SIM card) through Sprint for the past 1 & 1/2 years now and I want to upgrade it. My phone is thru the SERO plan (under my dad's account). I'm tired of this phone because it keeps freezing. I cannot upgrade it thru Sprint without having to switch to a more expensive plan, which my dad doesn't want to do. Is it possible for me to buy an unlocked phone and use the Intrepid's SIM card in that? Do I have any alternatives with unlocked phones? **NOTE: my goal is to get a new phone without having to switch the plan. Please offer insight.