The Eris has worked just fine for me for many months. I am not sure what issues you are having, but why don't you explain them firstly cause to tell you the truth, I hear people complain all the time with zero justification. You wanted a cheap Android phone and opted for the Eris. How do I know? I did the same thing coming from a Blackberry. But, I have upgrades available and you do not.
Here are your options:
1.) Add a new line of service.
2.) Pay full retail for the phone
3.) Buy a phone off of ebay or craigslist.
You actually have a couple more options available, but I am not a huge fan of cheating the system. Figure out your own options and next time, do some research before you buy. You had 30 days to love it or hate it. It would have only cost you $35 at that point. Now it's going to cost you more.
Or are one of these people who sees the latest and greatest come out and need to have it? If so, you should have bought the droid in the first place instead of the Eris.
Hope you get it resolved and I would make better consumer choices in the future if it that serious an issue you need to make a post about how to work around the system.