Some apps tackle big problems. Seamless isn't one of them. It merely syncs whatever you're listening to on your computer with your iPhone, saving you the trouble of having to tap through your collection to pick up where you left off.
WIRED Works with songs, podcasts, and audiobooks. Can sync back to iTunes when you arrive home (think entrance music).
TIRED Solution to a problem we didn't have. Works only if you're listening to a file that's already stored in both places.