Originally Posted by
Thysk
They actually can (as they have a list of miles needed for upgrade from certain classes), you just have to ask the right questions, or at least give them some input. What they mean is, that unless they know the booking class, they can't quote you anything. At that point, you can just ask whether there is any "O" availability (this is the upgrade class for non-Flying Blue Platinum members (as they also have the "Z" inventory at their disposal).
Just look on expedia.com for the ticket you'd like to book (expedia shows the booking classes), and then call KLM, stating that you'd like to ask how much it would be in FB miles to upgrade from booking class "(state here the booking class that you found on expedia)", to Business (booking class "O") and if they have any inventory.
Good luck on your travels!
Sadly that's no longer true, O class isn't confirmed miles upgrade availability. its a combination of cash and miles. the only way I've reliability found is to look at the FB site, first find out what the Business class cheapest fare is(classic fare, using the cost tool). then look at the flights on the day. This also isn't foolproof as I've also managed to upgrade on days where the classic fair wasn't available. But i'm plat, so may have extra access.