I accidently reset my IPone 4S, and now I want to get all the data back?

Ok, so my brother had given me his IPhone 4S, but it still had all these contacts of people I didn't know. And then when I wanted to post a picture or something on Facebook, it would always show up on his account… So I reset it. I filled out all of the information, and now I need to get the old thing back. Please tell me it's possible…

Haha! XD
Wait Your Serious?
Lol Jk But You Better Hope You Backed It Up Onto iTunes xDDD

Seriously? Couldn't you have just deleted the contacts one by one and log off his facebook so you could sign on yours?