So I don't know how much of this has to do with "unlocking" as it has to do with the tight coupling between Rogers and Fido. I just got a 3.1.3 5.12 replacement phone (silent switch busted on the old one) and I tried the steps outlined.
1) Downgraded to 3.1.2, Jailbroke using Blackra1n and couldn't use either card in the device.
2) Downgraded to 3.1.0, Jailbroke using Blackra1n again, and still couldn't use either card.
So doesn't seem like the steps shown worked. I then started fiddling.
3) Upgraded to 3.1.2, same thing.
4) Upgraded to 3.1.3, popped in my Rogers sim card (supposedly a Rogers phone) and the phone activated fine via iTunes. Unplugged from iTunes.
5) Popped in Fido SIM card, connect to iTunes screen pops up. Plug it into the computer, activates fine via iTunes.
6) Unplugged it, popped in Rogers SIM. All good.
7) Popped Fido sim back in. All good.
8) Popped a DIFFERENT Fido sim in. Once again connect to iTunes screen pops up.
9) Plugged in to iTunes, activated fine and SIM worked fine.
10) All 3 work fine now.