Bucks should trade for Udonis Haslem.
Simmons for Haslem and Posey.
Heat do it because they need to free up some minutes for Simien, and Simmons, while having the all around game that Posey does, he also is a deadly three point shooter which Miami really needs and sort of provides what 3 or 4 Heat roleplayers do in one player. I see him starting next to Wade for quite awhile. Bucks do it because they need the hard nosed hustle guy instead of a three point shooter, Posey fits their needs more. And Haslem gives them a great roleplaying 4 who blocks shots, hits the boards, runs the floor, and hits open shots.
Bucks go from a pusssy soft team to a hardnosed, gritty team while still retaining their ability to shoot the ball from deep, as both Posey and Haslem are suitable setshooters, with Haslem having range out to 20 and Posey out to 3.
And that's not even including your draft pick, and who you trade Magloire and Mo Williams for. Really, you've got an overabundance of talent. You've got a complete team and you still have 3 pretty big trading pieces that don't fit; these can be used to upgrade some spots I guess.