As far as I am aware, Android does not support this. There are ways around it depending on why you need it. For example, you can use an app called prefixer if you are using a calling card service which has a common number for, say, international calls. You can store multiple rules or different prefixes for different country codes. You can even get this to insert the original dialed number into the call log. Downside is that you will have two call log entries for each such call you make. Unfortunately, prefixer does not work if you also store individual's contact's conference bridge numbers and you wish to redial his number. It will not appear in the call in full - only the called number without the conference bridge pass code.