Not really second hand. I just want to buy a an unlocked phone because the ones provided by AT&T are garbage. I'm looking at the HTC desire, but I guess that's the phone I will get.
I bought a Nexus One semi-used (it was given to developer by Google who briefly tested some software on it and then sold it for 400$). This thing was basically in untouched condition when I got it and I have been really happy with it ever since.
Anyway I would suggest this. Get an unlocked phone (HTC seems good. I get the impression they are really trying to capitalize on the Android platform and are putting a lot into their phones, my Nexus One feels solid and well built, although honestly I havent handled their other models).
I know you can find factory unlocked HTC phones on Amazon for under 600, and surely some on ebay, although they may be slightly used (or to whatever degree).
Anyway call at&t and tell them, "your rates are high and I am not satisfied with your services." Quote them some prices from other providers and tell them you are switching because they are cheaper. My friend did this, and they immediately quoted him a price and plan which matched the opposition but wasnt officially offered by them anywhere that you can find. I would give this a try (although I dont what role the differences between his contract and yours may play).
You can quote tmobile for example. They offer a 30$ /month plan for talk only (smartphone or not). This is what I use. Its 500 "anytime" minutes a month which keep carrying over as long as you keep the plan active. There is also no contract so you can discontinue it any time. If you want a data plan along with that, they only offer an unlimited plan for smartphones which comes to 60$/month for unlimited talk, text, and web.
Basically you want at&t to offer you a sim card only plan. Dont let them get involved in the fact that you have a "smartphone" because then they will want to pitch you xyz and blah blah blah about data plans , etc. Which is really none of their business unless you want it to be. Just tell them "I have my own unlocked phone, what are the service options you can provide me? If they arent to my liking or better than my other options I want to go somewhere else." See what happens...
By the way the desire looks good to me.
Here is an unlocked one from Amazon.
I imagine its possible one or two more cutting edge Android phones may appear before Christmas, but if waiting to see what happens is out of the question, I would go for an unlocked desire or Nexus One, if you can find it.