In Windows Mobile, if you have to call a number (in your contacts) followed by an extension, you can simply put commas after the phone number in your contacts. For example, if you want to dial Extn:1234 after reaching (123)-456-7890, you can simply put 123-456-7890,,,,,1234. The commas act as a pause breaker. This is particularly useful while you are driving in a car.