After poking at the Samsung BlackJack and other various models, I picked up the Cingular 8525 last week. It's the first Windows Mobile phone I've ever owned. Normally I lean towards phones running Symbian, like my old Nokia E62, but I was getting tired of the 5+ second delays anytime I tried to open an application. I loved having a free port of PuTTY, and the Symbian Developer Network was totally fabulous, but I felt it was time to try something new.
The Blackjack was very shiny - nice form factor, etc. The battery doesn't usually last very long though, especially not when you're pushing the Bluetooth and 3G at the same time. I'm not too big on cell phone cameras, but the 8525 scored another point with it's 2.0 megapixel camera versus the Blackjack's 1.1 megapixel. The 8525's keyboard is a lot easier to type on, as well. I wanted more of a business class phone, and the 8525 definitely falls into that category. The Blackjack seems more consumer level.
What almost killed the 8525 for me was the lack of support for PAN. A friend confirmed that the latest firmware update added support. MacOSX's latest update, 10.4.9, finally added PAN support as well. This makes setting up an internet connection over your phone super easy. I found that after the update, you have to delete and re-pair your phone to make the 'Connect to...' option display in the Bluetooth menu.
Totally loving this phone so far. More info later.
I had the blackjack for a while and it just had a lot of issues. Battery life was so bad they had to give it out with a second battery. The OS and Java implementations just had a lot of issues. Got rid of it and got the 3125.
Btw here is some great info and hacking links for the 8525.
As well HTC is supposed to be coming out with an even newer version of the 8525 style thats only 17mm thick.