Iphone 3 problems HELPPP!?

Just recently when alltel went to At&t i decided to get the Iphone 3. Yes its a refurbished. & right away when i got it i have been having issues with it. I've been having problems were the brightness doesn't always like to go on right away, it can b a whole hour before it turns fully bright! At my mom's house her wifi is on all the time and i have my old ipod and it connects to the wifi here all the time with no problem, my iphone is the exact opposite, it will every now and than connect but after aout 10 minutes it will stop connecting. & now today i was trying to send a message to one of my friends and it will get to bout 80% then it will have a message error. Ok i checked im on 4 bars. I have mm messaging & group messaging on. I have 3g on but its being a butt. & The problem i have had with At&t is that my dad signed me up on a data service and i can't go on the internet! Ok so we spent money on nothing? Im real happy now. I have been wanting to bring my phone into At&T but they would probably say i did something to it and will have to buy a new one. Ok im only 15 im broke and this phone i have been really gentle with, i clean it regularly and i've only dropped it once but it has a hard cover over it. Help! :(