Timing has not been announced yet. Since they're still working on it, probably even Motorola/Verizon insiders don't know for sure.
Hi Trouble! At this time we do not have any release dates for 4.0/Ice Cream Sandwich on the Bionic. Once it is released, it will be automatically pushed to your phone. You will also find info on vzw.com/support about the update details once available.
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Motorola finally provided an answer this morning: "Rollout begins in early Q3 2012".
In this official notice posted on Motorola's website: Motorola Android Software Upgrade News
And "early Q3" should mean "July"!