As with any ROM update, everything but the boot loader will get wiped.

But to be honest, I wouldn't hold my breath. All PDA phones I've known (at least through HTC, the 6700's maker) have been released as standalone updates available online. Even if Sprint did the upgrades themselves in-store, all you need is a standard USB cable. I don't know what else that tech would need and why he couldn't do it now. Attach USB cable, run exe file. Pretty simple.

I hope its true, I'm dying to see if A2DP is included. But, as I said, I wouldn't hold my breath. When someone actually sees the update on Sprint's website (I checked, it wasn't there), then we'll know its here. All this "inside info" stuff rarely pans out.