Here what I did, from a clean system w/o BlackBerry Desktop Manager.
1. Perform a clean uninstall via
BB KB KB-02206.
2.
Install BlackBerry Desktop Software v3.6 [SP3](Click on download link at the bottom of the page)
3. Perform a FULL device BACKUP!
4. Download and install the
BlackBerry OS 6230_6280-v3.7.1.41_P1.6.1.41 (6230 Handheld Software Bundle 3.7.1.41)
5. Perform a FULL device BACKUP!, name it something different.
6.
Download the AT&T BlackBerry OS 4.0
7. Erase the vendor.xml file, or rename.
8. Install the AT&T 4.0.
9.
Install Berry 411! (Mad props. to Phil Bogle, I love it!!)
Please note, this worked for me, might not work for you.
If you get an error msg. or something post it.