I have this phone that I bought a long time ago (like 3-4 years ago). It was one of the first digital phones to hit the market (Siemens S12). It is the type that takes the SIM card. I haven't used it for over 2 years, its just been sitting in a closet the whole time. So last week, I go dig it out of my closet and take it up to a new service provider (Cingular). I buy a new SIM card and some prepaid minutes on the new card. Now the only problem is, my phone is not wanting to work properly, so after talking with and going round and round withSiemens and Cingular for days about getting this phone to work, I've just decided that I'll just buy a new phone. This one is way outdated anyway. So now, I'm not really looking to get anything fancy, just want to be able to talk, but don't want anything that is soon to be obsolete either. How do I know which ones I can buy and just be able to put my SIM card in and use? I know that most places try to sell you the phone with a plan already on it. But that's not what I want. I am looking at phones on eBay, and I notice, some of them say "unlocked" on it, or whatever. How do I know if I buy a phone will I be able to just pop my SIM card in and use it? And even if I can't, what do I have to do to be able to use the phone?