Why can't a get Edge or 3G?

I have a Samsung Solstice, with an AT&T provider. I've contacted customer service which couldn't help me because they need the last 4 digits of the payer's social security number. The payer being my sister. I don't know it, so they can't help me. Whenever I try to send or receive a multi-media message, it says "Sending/Retrieving failed. Connection refused. Retry?" It doesn't work without the Edge or 3G connection. I've been all over town, and can't get one anywhere, while all my friends and family can. Can anyone help?