MacObserver this week posted an absolutely awesome tip detailing how to auto-dial phone numbers with extensions into your iPhone address book.
Forget having to remember someone's extension number, or trying to keep it handy and accessible with a note, iOS 6 takes care of all the dirty work for you.
To get started, go to the contact info of someone with an extension or create an entirely new contact. Hit the "Edit" button in order to make changes to the contact's information page.
When you attempt to edit a contact's phone number, you'll be presented with the following screen.
If you tap the lower-left button with all of the special characters, you'll notice that options for "pause" and "wait" will appear where the "4" and "6" used to reside.
A pause adds a two-second delay, which is indicated by a comma.
You can add as many pauses as you like, and then you'll type in the extension at the end. So if you know, for example, that a certain business makes you wait six seconds before you can punch in someone's extension number, just insert three pauses as I've done above, and your iPhone will dial the extension for you after that amount of time.
It gets even better because the "wait" key will allow you to pre-program in a number of extensions, thereby saving you from having to wait and traverse through a frustrating tree of automatic menus.