I worked retail for a long time, including an Apple Store. I cannot remember the policies at Apple when I was working there, but most places will not take a verbal approval code.
If the person on the other end of the phone (generally you get to them by calling the 800 number on the back of the card) has the ability to run the transaction, they have the ability to clear whatever prevented the card from going through the first time. They would have to - they have to clear the hurdle before they can run the transaction themselves.
So policy at most places is that the telephone operator clears the issue (usually it is a daily spending limit that card issuers never mention) and then the store runs the card again. There was no procedure for manually entering a verbal approval code.
My memory of Apple Retail (this was '04-'06), however, is that they had almost every contingency covered. The POS machines all had USB modems attached so that in case the Internet went down at the store, credit cards could still be processed. We even had the old CH-CHUNK imprint devices when everything went pear-shaped. I do seem to remember having the ability to enter a manual authorization code for a credit card transaction. It is Apple Retail - there are supposed to be no hurdles keeping a Specialist from keeping a customer happy.