Guys, this has nothing to do with the trade. Belkin is just using it for leverage because the other owners want him to sell his stake. (He's being outvoted 8 to 1 among the owners).
As far as the trade, the Suns have said publically that they have to get compensation for JJ, whether it be a trade or matching the contract. They have given all appearances that they WILL match the contract.
So, Atlanta gives up three things:
1. A player that has been an incredible underachiever on a horrible team.
2. The Celtics' pick (via the Lakers) which is top 10 protected this year and will likely be in the 13-18 range in a weak draft. If the Lakers finish 10th or worse, that pick goes to 2008 and becomes the worst of the Celtics' three picks that year (Celtics, Cavs, Lakers).
3. Their own pick in 2007 because they're not likely to make the playoffs this coming season. In 2007, it's lottery-protected, so the Hawks won't miss out on a franchise player that year.
At some point, the Hawks have to assume their young players will improve. They will also have a ton of money in free agency next year to improve the team, plus their own draft pick. They already have a ton of young players and are one of the few teams in the league that don't need to get any younger.
It's definitely not a steal for the Hawks, but it's less than the Nuggets gave up for Kenyon Martin and a shorter contract.