This is a big topic for me...phones and assorted other nerd gadgets.
I have a Sprint PPC6700 and my wife has a Samsung Blade. They're both BT capable. I've been using BT headsets for about a year or so now, and here's the list.
1. Plantronics M3000 - Bar none, the best headset I've ever used. Sound quality was excellent, battery life was great, and it NEVER lost connection. Literally. I only remember one occasion when it lost connection to a paired device. The downside? It was big. Far too big for most of you who I've met. I could get away with it because I have an enormous melon.
2. Motorola H700 - Originally purchased for my wife, it was perfectly sized, but it didn't connect real well with the Blade, and she couldn't hear on it at all. I didn't bother trying to wear it.
3. Jabra BT800 - I tried this one for myself, and scrapped it after 20 minutes. It just wouldn't hold a connection at all. Cool features (caller ID screen) or not, if it doesn't actually connect until 7 seconds after you answer the call, that translates to a lot of dropped calls.
4. Motorola H500 - Worked fairly well, but too big for my wife's head. Volume could have been louder.
5. Cardo Scala - This one works very well, and I'll continue to use it for quite a while, I think. It sounds good, it fits your ear very well, good battery life, and good connectivity. The best part? $45 shipped with a car charger and wall charger. My wife is using this one right now. We alternate headsets.
6. Bluespoon AX - By far, this is the tiniest little headset I've ever seen, and once you get used to it, it actually works fairly well. It's an in-the-ear type thing that doesn't have an ear sling, which is nice. I'm starting to notice that it can mess with your sense of balance after wearing it for a long time. I took it out of my ear this afternoon and was a little dizzy.
So, I guess we've had six headsets by my last count, not seven. However, as the Motorola H5 Miniblue gets closer to coming out, I'll probably find a way to give one a test drive.
I think that the H700 had a problem with quality and volume because we got an early version of the Blade. They released an update a week or two after we returned the headset that might have fixed the problem.