A dial code is not a common phrase, and doesn't seem to have a specific meaning. People seem use it to mean a set of dial codes that you press on a phone to access parts of a phone connected system, such as a voice mail system, or to access features of a phone system, such as turning caller id on and off. An area code is a part of the phone number for a landline phone, that is associated with a physical area. Typically a full phone number will consist of a country code, an area code, and a phone number. If you are calling another phone in the same area, you only use the 'phone number' part. If you are phoning a phone in the same country, you use the area code and the phone number, etc. I think that the area code for beijing is 10, and for shanghai it's 21. Mobile phones have a different system, as they are not typically fixed in a specific area, but still have a country code to access them from another country.