How do you download contacts FROM the iphone and be able to import them into another device/application?

Is there a way to access the address/contacts book in the iphone so that it can be used in, for example, a gmail account?

I'm just unsure of how the iphone syncs contacts. Is it two-way (new contacts on the phone and new contacts on the computer are sent BOTH ways) or are contacts just sent TO the phone?

Thanks!