Why can't I access the APN settings on my Straight Talk bought Iphone 4s?

Please! I have been trying all day to figure out what's wrong with my phone and ever since getting it, the phone has been nothing but trouble. Let's start from the beginning. I had purchased a Straight Talk Iphone 4s from Walmart, hoping to cut down on costs. When I received the phone, it had said that I needed a SIM Card, which I didn't have. After buying one and waiting another day or two, I thought I would finally be able to have the phone. However, as I was setting up the directions had said that I needed to put in my APN settings in order for me to have internet without Wi-Fi and receive/send picture messages. It told me to turn off the Wi-Fi and other things, go under general settings and find the network tab. There was supposed to be a place where I could easily put in the settings, there wasn't.instead of "Network" written I have "Cellular" and there's no place for APN. I had searched on multiple sites and watched videos from Youtube. I downloaded everything I could and nothing helped. I finally called customer service and they told me to search for "iapnupdatetfdata.straighttalk.com" on Safari and install whatever I was supposed to, however Safari wouldn't let me access the page. I know exactly what I'm supposed to put in the APN settings, if I'm ever able to get to them.

Give this a try http://www.unlockit.co.nz/unlockit/

just check their old blog post and follow instructions. It can change your apn even if your iPhone does not allow you to.