I too have had a problem with my 4.1 upgrade.
Here in Nebraska, the 2 biggest players were Alltel and Cellular One (Western Wireless). Of course Alltel bought Western WIreless, and are in the process of merging.
On Tuesday, Alltel began merging towers in our area, and I went to roaming, with Data Access Refused. I called Blackberry support, and they found the PRL was wrong. They would not help with the problem, since I had the newer OS from another company.
I re-installed the 4.0 software, updated my PRL, and have no problems.
I like the OS changes, seemed to make the user experience mch better.
Blackberry Storm2 (Verizon)