Okay, spiffy new N900 in hand here, and an old-school Nokia 9300 is awaiting decommissioning. How do I unload my old contacts and reload into the N900?

Both devices support bluetooth, and I can pair them. I've found the "Transfer and sync" button under "Settings". But now what?

It occurs to me that I don't know what "sync" means, not really. Will it suck the existing data off my Symbian device and populate the Maemo contacts database? Or will it suck the empty database out of the N900 and zero my 9300? (Ohno!)

What does sync do?