Addendum to the speaker phone: Please don't listen to your voicemail over the speaker. Also, when on hold for the helpdesk, please don't put the hold music on speaker. I know the wait is horrendous, but sound really carries and it makes it difficult for your co-workers to hear their own phone conversations.
Also, when having a business related discussion in the aisles of the cube farm, please try to keep the volume as low as possible. Your co-workers may be on the phone with a customer who shouldn't be privy to that information.