The Satechi Swift BT Speaker is a surprisingly affordable little speaker (at just $29.99) that performs quite well. It's small and fairly stylish, and though its functions are about what you'd expect from a Bluetooth speaker, the Swift accomplishes them with an understated flair that I really appreciated.
Setup is pretty standard for any Bluetooth device. You need to turn the speaker on, hold down a button for six seconds to put it into pairing mode, and then flip your iPhone's Bluetooth on and pair it up. Once that's done, the Swift works almost automatically. Whenever you're in signal, the speaker will connect up to the phone, and you can share audio signals between the two devices.
The best use I can think of for a speaker like this is just to have it sitting on a desk at work or home, someplace where your hands might be typing or writing rather than holding your phone all the time. Whenever a call comes in, you can just press a button on the Swift speaker to answer it, and then it all works as you'd expect. Speak into the integrated microphone, and listen to the other side of the conversation from the speaker.
In my short time testing the Swift, I found that it worked best the closer I was to the unit, so yelling across the room probably isn't ideal. But again, if the speaker's sitting on your desk already, you should be able to place it close enough where you can speak directly into the mic without a problem.
You can also use the Swift for voice dialing, and you can redial from the speaker, reject a call (by holding down the button for longer than usual), or even send the voice back to the phone itself. The mic on the unit can also be muted, which might be ideal for long conference calls. Finally, you can also stream music to the speaker over Bluetooth -- the tunes I streamed sounded just fine with an impressively solid bass. The quality isn't incredible, but especially if you're already in a work environment, it's good enough just to have something to listen to. If you really cared about audio quality, however, you'd be much better off investing in an actual stereo system or, more likely, some quality headphones.
I was quite impressed by the Swift speaker. I don't normally bother with speaker calling, but I could definitely imagine keeping this on my desk and using it (especially because my cell phone's signal happens to be terrible where I usually sit; with this, I could keep my phone across the room and answer it when it rings right through the speaker).
The one big drawback is battery life: The Swift speaker itself has up to 300 hours of standby time, but only three or four hours of talk or music playback time. The speaker comes with a USB charging cable, however, so it's possible you could just find an open USB port and let it stay plugged in. The Bluetooth service will also cost your iPhone's battery a little bit, but depending on how often you use the speaker, that cost may be worth it.
For a price of just $29.99, I highly recommend Satechi's BT speaker. If you've been looking for a way to more comfortably deal with your phone, especially at a desk in a private office or someplace where you won't bother anyone around you (please don't be that guy on the speakerphone in a bunch of cubicles), the Swift speaker could be really useful. As it is, I can see myself using it in my own work. The next time you call me, I may just press a button on this little device, rather than having to run and get my phone from wherever I last left it.