Nokia Lumia 900 not connecting to internet away from wifi

[aywowww]

I got a Nokia Lumia 900 from a friend for my birthday. I had a ZTE Whirl [bought from the straighttalk website] before but didn't like it. So I bought the Lumia 900 from a friend. She had it from AT&T [it was already paid off]. Since I couldn't get a different sim card, I cut down the sim card down [which was the sim card I got with my whirl] to fit in the Lumia. It worked fine [after getting an unlock code from AT&T] but I discovered that I couldn't connect to the internet when I was away from wifi. The wifi works perfectly, I still have the same number and can send/receive text messages, but I can't send/receive picture messages or access the internet when not in wifi. I checked to make sure the data was on and it was but it still wasn't connecting. I looked around on other message forums to see if anybody else had this problem. It seemed that the Lumia 900's were having connectivity issues and somebody posted a tip on entering a new APN which I did on my phone but it still didn't work. I'm wondering if there's anything I can do to fix this. Is there something I can do myself or will I have to contact StraightTalk support to help? Like I said, everything else works fine, I just can't connect to internet using data instead of wifi.

[Jhonally_ST]

Hi aywowww. My name is Straight Talk Jhonally. Sorry that you’re having a problem. I’m going to try to help you now. We need to take this issue offline, so I can address it further. I will contact you directly with a private message. Thank you.