Seemingly, one big plus in buying the ticket from UA over the phone, per my one experience earlier today, is that UA can see if the upgradeable inventory is available before purchasing the ticket and before pulling the miles for the upgrade cert. However, even if the upgrade inventory is there, UA sometimes may not be able to confirm that upgrade as they need to get the final ok to upgrade from LH. That approval from LH can be immediate, or take up to 48 hours per the UA phone agent I spoke with. Overall, much better\easier than I thought it would be (although I didn't buy a ticket).