It is common nowadays to dial a number and then dial some other number (like an extension or another number if the first number is a calling card, 1800 number or something..). You can easily do this automatically via your contacts. For example, I have an international calling card. To call an international number, I have to dial a local US number (say 1234567890) which then asks me to dial the international number (say 0987654321) followed by a # key. Before, I used to dial the first number (saved in my contacts) and then I used to dial the international number and the #. Now, I just saved it as 1234567890,0987654321# in my HTC HD2 contacts. And I simply call from contacts. The phone first calls the number before the ‘,’ (comma) and then ‘pauses’ once and then dials the rest of the numbers (including the #). Note that each comma represents a pause. So if you include two commas, the phone pauses twice before dialing the following number.
Hope this helps.
– C S