Using the speakerphone can be particularly handy when you're driving and you don't want to hold your iPhone against your ear, so you can keep both hands on the steering wheel. The Mute feature is also useful for times when you want to say something that you don't really want the caller to hear. You can pretend to make a call to your boss and launch into a tirade of insults (with the Mute feature turned on, of course) so that your co-workers will think you're brave (or just extremely foolhardy).