The phone I got through T-Mobile required that I have 2 months of paid service with them before they would unlock. I called them, requested it be unlocked and 1 day later got a text message that it was done. Nothing changed. I have not used it elsewhere yet, but you would "lose" some programming in a way as a lot of info that you have stored or saved on the phone is tied to that SIM card. However I believe that when you pop the original SIM back in, it's all still there. I know with my phone and service a lot of my info like my address book, calendar, notes, photos are all stored on the web and I can access them through T-Mobiles site.