Can i switch phone numbers in the same mobile phone company?

I currently have a t mobile line that was signed up a while ago for me by a former friend iv got about 17months left in a two year contract i now want to change the information and billing to my own is that possible?In the alternative I'm ready to terminate my present contract and purchase another t mobile line but id like to keep my present phone number when i do that is this possible?|||I am sure T Mobile can do that for you.