May be this is a celebration too early - only time will tell.
So I was with blackberry and had a great bluetooth experience with Z1. Then I bought the Cingular 8525 (HTC - Hermes) and started getting guaranteed bluetooth disconnects mid-call - 99% of time the disconnect happens within 2 to 3 mins (this is the bluetooth disconnection, not the actual call disconnection with the other party - most of the times you can continue the conversation by using the phone set). Everything else was great. Returned the unit after reading many posts in the internet how WM5 phones are notorious for not maintaining bluetooth connections while in-call. There are other issues while not-in-call with many phones, but the WM5 phones drop bluetooth connection mid-call - very frustrating. THis is not just with Z1, but also with Audi, BMW, Acura bluetooth kits that I read in various web-forums.
Just got the Treo 750 (WM5 with Bluetooth 1.2) and was very nervous that if I get the same bluetooth connection - it will be a must return! Guess what - I made multiple calls using the Z1, one of them lasting more than 15mins and all calls stayed intact. I will post more details later after more calls over multiple days.
The things different about Treo 750 and Cingule 8525 in the bluetooth department: Treo 750 Bluetooth is v1.2, 8525 has the v2.0.
Another interesting observation was that: during the call duration, the screen light stayed dim, not completely turned off. I don't remember if the other WM5 phones completely shut off the backlight and I am not even sure if there is any dependency but if the system trying to conserve power by shutting off not only backlight, but also some services (including bluetooth?).
I really do hope that I will come back in a few days or more and say that bluetooth still works.
I haven't figured other features on the Treo bluetooth (like complete address book transfer etc. yet - I just wanted to test the disconnect issue rightaway).
cheers
Phal
Z1, IPod, BT, XM-NAV, both remotes (SR1 and the other rear one-forgot the name!)