The average size of a US military spy satellite is roughly as big as a large pickup truck. Soundwave size is relative to that.... I would say roughly the size/bulk of Ironhide... probably taller since it seems that Ironhide appears to be hunched over most of the time (in battle stance).
Without an Earth mode or some pictures of him standing next to the other robots it's hard to say. With his alt mode being Cybertronian he could be anything from the size of a tape deck to as big as a ship.
The first guy had things that contradicted first what we've already seen and then his second report contradicted what he said in the first one, and the studio guy, well...THEY WOULD NEVER GIVE AWAY STUFF LIKE THAT. It would cost them their jobs. So yeah, bit suspicious.
If Soundwave was originally supposed to turn into a black pickup truck (Concept art we got a while back, Orci said it was scrapped from the script), then he's around 20-23 feet in height, same is Ironhide or Ratchet.
