International Direct Dialing Code (IDD or Exit Code) is the prefix code for making international phone calls. For example, to call China from USA, you need to dial "011 + 86 + phone number", in which the 011 is the International direct dialing code of the United States of America (and the 86 is the country code of China).
For more country codes see: List of Country Codes for Making International Phone Calls.
~: wait for a second tone.