Under some conditions cell phones' speakerphones are absolutely shrill and can be heard for quite a distance, more so than a regular telephone's speakerphone. I've heard it in restaurants, airports, public transit, etc. Even in parking lots, it seems like the noise cell phone speakerphones carries much further than normal human voices.

I'm with [MENTION=52076]dayone[/MENTION] -- a headset / headphones are the best solution. You also never know what the other person's story is. If you've been on planes for 15+ hours and are now many timezones from where you started the morning, you want sleep, even if it's 10am local time.