Here is the one I currently own.
http://reviews.cnet.com/headsets/sony-dr-bt22-wireless/4505-13831_7-32780196.html?tag=box4505
I also posted a review on it if yo want to see it. I prefer the over the head headsets and earbud headsets because they both offer stereo sound. I have a Nokia N75, and it has A2DP (the music streaming bluetooth profile) and AVRCP (the ability to control my phone from my headset). Any bluetooth accessory for my phone I buy will have to have both of these available to me, as well as the ability to output stereo sound.
I think I mistakenly said earlier that A2DP was the stereo profile. After doing more research on the matter, I discovered this. I have quoted it directly from Wikipedia.
"This profile defines how high quality audio (stereo or mono) can be streamed from one device to another over a Bluetooth connection.[1] For example, music streamed from a mobile phone to a wireless headset."
The T505 you posted a link to only outputs in mono sound. And as I have said earlier, it connects to the car's stereo using an FM transmitter. I planned on using this to connect to my car, but a) with it being a cell phone, it gives off radiation that interferes with the FM transmission, and gives you that galloping sound you hear when you put your phone too close to the television.
FM Transmitter: http://www.griffintechnology.com/products/itripautouniversalplus
If I were to use a connection to my car stereo to achieve handsfree status, I would use something like this, but once you do that, you are once again getting into new head unit price territory, so I would still go that route.
Hardwired Bluetooth setup: http://www.crutchfield.com/App/Product/Item/Main.aspx?g=324750&i=333CK3200L&tp=8397
"It's great that we have so many options when it comes to taking hands-free calls."
Very true. But for me, I just want entirely too much for me to be happy with an addition like this. It all comes back to what you want out of your setup. If all you want is the ability to talk handsfree, and play a little music, then this is a viable option for you. For me who wants stereo sound, the ability to see who is calling me, and without any interference, I need something a little more robust.