Addendum: if we were to trade for Smith though, it would involve Pierce and the first almost certainly. They're not really ideal trading partners at this point.
Look at it from atlanta's standpoint. Acquiring Pierce is a lateral move, and one that will cost at minimum 5 million for the buyout or 15 million for a 1 year rental of an aging Paul pierce.
For them to do this, they'd need another asset beyond Pierce back. Likely the first and maybe more; the trade exception they'd get in a sign and trade is a valuable asset in and of its self.