Recently 5.0.0.348 for the BlackBerry Bold 9000 was leaked. I installed this on my BlackBerry and all was well, until I traveled to the US and put my AT&T SIM card into the device. It then gets into a reboot cycle the minute a network connection is established. I am speculating that something in the AT&T service books is causing the device to reboot. Potentially their service books are not updated to work with this version of OS5 on the Bold.
If you are using a Bold 9000 on AT&T, and you are considering upgrading to this leaked version, you may want to give it a miss. That said, I mainly travel in the Washington and Oregon areas, so it is possible that your mileage may vary on AT&T across the states.
If you have this problem, it is easy to fix, simply turn off your devices wireless connection, then it will boot up, and downgrade to a different version of firmware for the device. Inconvenient – yes – but then this is beta firmware.

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The Best version is os 5.0.0.314 with the .348 radio for At&t users.
Thanks, that is helpful. I have tried .411 on AT&T as well, and that seems to work without the reboot loop. Do you have any experience with that?