Sometimes waiting for automated phone menus and dialing extensions can be a real drag. Luckily, the Apple iPhone has an easy way to automatically dial extensions when needed.
All you need is the contact you're trying to reach and the relevant phone number and extension you'd like to add to the contact information.
Open contacts and select the person's number you'd like to add an extension to, then select "Edit" in the upper right hand corner.
Now select the phone number that requires the extension. Touch the "+*#" button in the lower left hand corner of the screen.The "pause" button will appear in the center of the bottom of the screen. Touch "pause" and a comma will appear in the phone number. Enter the extension.
Finish editing and you will see the phone number now followed by a comma and the relevant extension number. Next time you dial the extension will automatically dial.