Speaker phones are the worst invention ever! They are immensely dangerous in the hands of complete idiots. Why would someone create such a device? No one should be subject to the torture of overhearing your boring meeting, or your sappy conversation with your lover. Sure, they may be useful for having a conference call, so restrict them to conference rooms! Don't put them on cell phones, in the hands of the same people who text and drive. It's a recipe for disaster.
Worse yet are the absent minded morons who put you on speaker phone, without telling you. They aren't the ones who suffer the unintended consequences when you blurt out something meant for their ears only. Not the ears of your girlfriend and her best friend who you think is hot. Certainly not the ears of your boss who was in the same room. And not the ears of the friend whose surprise party you're planning.
A word to the wise: do you see that convenient speaker phone button? The correct answer is no, you don't see it. Forget that it's there!