Since Smith has been a good soldier in his contract year and hasn't make any demands to be moved, I don't think ATL will do anything with him at the deadline. They're strategy has been to clear up cap space to make a run at CP3/D Ho and some of the lesser FA s this summer.
The only way Boston gets Smith this summer is if he convinces Ferry that he will sign with a team with caproom and the Hawks will get nothing for him. Then he and his agent can finagle a S and T, assuming the Hawks like Green and one of Lee/Bass/Terry.
ATL has only $21m on the books next season and Horford is an star center at $12m, They would have room for two max FAs, and could conceivable keep Josh Smith, and S and T Horford for Howard (who would tell the Lakers he's going there anyways if they don't agree to the S and T) and sign Chris Paul outright.
If Howard and Paul don't come on the market, the Hawks will re-up Smith, add a SG like JR Smith, and maybe a low post threat big like JJ Hickson.