Ok, after reading through the thread I see what you are talking about. I posted that from the mobile forums and likely didn't read enough.
I actually answered the OP's question but he asked it again anyway. I post to other forums too and likely thought I was answering a different question than that of the one here. Regardless, my mistake.
The answer to the OP's question is that an unlocked FIDO device will NOT connect to UMA on Rogers or any other network other than FIDO (if they even had UMA.) I said this in post #6. Changing the OS will not do anything, either. The FIDO device will not have the proper UMA profile set up in the engineering screens. It is possible to add UMA functionality to an unlocked device from another provider but it requires techniques that are above most people's ability. That said, if you think it is within your ability I have written posts on adding TMobile UMA capability to other branded devices. For example, I have an ATT branded Torch and I have to complete this process each time I upgrade the OS on it. See the post here: Get Your Unlocked 9800 Torch Working on TMobile with Browser, UMA and DM Tethering
I'm sure there is info out there on where to get certificates for Rogers and the proper Rogers server info to enter in the Engineering Screens but I don't have that info off hand.
I hope this clears it up.