Got BB Connect working on Cingular 8528, but...
I managed to get BBC working but I've had some big problems with it, I think I am going to give up and go back to carrying my 8525 and a company BlackBerry. Here's what I did, so others can benefit and continue to push the envelope:
I called Cingular and ask them to activate the BlackBerry Connect plan, and turn of the previous unlimited internet plan. I lied and said I was using a Nokia Communicator 9300 (like another thread here told me to, because they're not "supporting" BBC on the 8525 yet). The operator confirmed what I had read elsewhere: BBC would only work in 2G. She also said that having both data plans may cause problems so I agreed to keep it simple and just have the BBC plan, at least while I got it working. However, maybe it's my location (New York City) but I still got 3G on the BBC data plan and the BBC software picked up email fine over 3G (UMTS).
I downloaded and installed the BBC software for the 8525 and the Windows desktop software for BlackBerry Connect. Version 2.1.2.9 of the desktop software, 2.1.2.16 on the 8525. Before installing, I quit (but didn't uninstall) the existing BlackBerry Desktop software. The new BBC Desktop software seemed to pick up on some of the preferences as the old BB Desktop. Eg, it knew the PIN of the old BB device, and offered to switch to the PIN of the 8525 running BBC. After doing the setup, the 8525 started receiving corporate emails. No IT department involvement (much to my relief).
I had chosen to sync the Calendar. I plugged the 8525 into the PC and clicked the "Connect..." button in the bottom-left of the BBC Desktop software window. It took about an hour to download all my work calendar to the device, wiping out the previous calendar that was there before (I had all that data synced to my computer at home, so I'm not worried).
This is where the trouble starts. Sadly, my company is forced to use Lotus Notes as an excuse for an email and calendar program. This means that the calendar becomes corrupted as often as it can. There are certainly broken calendar entries in there, but I'm not going through several years of calendars to remove them. I've tried setting up the archive "feature" to just remove old calendar entries but it doesn't work. Don't talk to me about this.
This doesn't cause problems on the BlackBerry device because it's configured to only sync the most recent X days of data. There seems to be no such setting on the BBC software, though. So I get between 1 hour and 2 days of peace before the 8525 complains about invalid calendar entries. Often they are 1 day events (like birthday reminders) that it complains cross 2 days (starts on 1 Jan ends on 2 Jan) or they seem to have lost the connection with their repeating entries. With a bunch of error dialog boxes filling the screen the device freezes.
I restart but, even with the BBC software set to "Suspend on Restart" the 8525 gets hung on Invalid Calendar (this time displayed in the title bar of the screen, next to the Windows logo). The only option is to restart with the memory card ejected (where I had installed the BBC software), then put it back in and uninstall the BBC software from the 8525.
Sometimes the software didn't uninstall completely, I had to re-install and then uninstall to get it all out.
When it worked, it was pretty good. Not carrying 2 devices was a relief and using a nice big keyboard on a narrow device like the 8525 is more comfortable for me. However, I didn't get attachments to download (yet) and it only seemed to have 2 screenfuls of emails, rather than days and days on the BB device. I don't know what caused this. Is the BBC software storing data on the memory card? Perhaps not, so it maxed out at a small amount?
Also if I ran IM software on the 8525 it permanently blocked BBC from connecting. I still had my personal email sync every 15 mins and the 2 services managed to play nicely.
I would gladly try a newer version of the BBC software, if it seemed to address this problem. I see other posters referring to later version of the BBC software, so maybe that will help.
I also read of an upgraded Cingular ROM for the 8525, possibly being released next month. This is said to include activation of the PTT button and a "Download BlackBerry Connect" link. I'd like to think, it's a more stable version but it's anybody's guess until we try it.