Just A Question, Need Help ASAP

I just have two quick questions. I'm not new to owning a cell phone, but I don't know much about them. I have an Audiovox COM8900 phone through US Cellular. My friend has Edge Wireless and a Nokia 5140. He switched providers and still has insurance and said if I gave him the $25 he would get me a new Nokia 5140. So my first question is will the 5140 be able to work with my US Cellular account? Next, I've heard a little bit about unlocking phones with a code or something so that they will work with all providers, is this true?

I really need some help with this, I don't have a whole lot of time to decide if I want the phone or not, so any help would be greatly appreciated.

I did a little more research, and I'm actually more confused. I was told that I could not do it because my phone is CDMA and the Nokia is GSM. But, US Cellular carries both CDMA phones, and GSM phones. So would the Nokia work?

us cellular is a cdma service provider no sim card.
nokia 5140 is a gsm phone have sim card.
unless you have nokia gait phone that carrie both gsm and tdma network but not cdma.