Today I'm going to cover an iPhone tip - you iPad users will have to pardon my digression, because this is a pretty nifty tip: automatically configuring your iPhone to dial an extension. The magic comes by inserting a "pause" during the dialing process, which your iPhone permits. Here's how to do it.
Go into the contact you'd like to edit, or create a new contact.
In the phone number area, enter the main number of the contact. Then press the +*# button, and pause will appear where the number 4 usually sits.
Each time you press pause, the iPhone inserts a comma - the more commas, the longer the pause between the time the call is answered and the time that the extension is dialed. Enter as many commas as you think are needed.
Then add the extension. Press Done.
Now when you go back to your contact, you'll see the phone number like this, to let you know that the iPhone will directly dial the extension the next time you need to call that number.