The latest official OS for Alltel is 4.5.0.127 on the Alltel site. I am still running 4.5.0.89 as everything is working well and I see no reason at this time to upgrade.
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If you are going to run 4.5.0.131 you can download it right from the Sprint site even if you don't have a Sprint phone. Just make sure that you delete the vendor file before you load it onto your BB.
Posted from my CrackBerry at wapforums.crackberry.com