A closed telephone numbering plan is one in which the subscriber's number is a standard length, and is used for all calls, even in the same area. This has traditionally been the case in small countries and territories where area codes have not been required. However, there has been a trend in many countries towards making all numbers a standard length, and incorporating the area code into the subscriber's number.This usually makes the use of a trunk prefix (usually '0') obsolete. For example, to call Oslo in Norway before 1992, one would dial:

This changed to 22 xxx xxx, so that an eight digit number was used for all calls. In other countries, such as France, Belgium, Switzerland, and South Africa, the '0' is retained for domestic calls, whether local or national, e.g.:

In Italy the '0' has been incorporated into the subscriber's number, and must be dialed internationally, e.g.:

While the use of full national dialing is less user-friendly than only using a local number without the area code, the increased use of mobile phones, which require full national dialing and can store numbers, means that this is of decreasing importance. It also makes easier to display numbers in the international format, as no trunk code is required - hence a number in Prague, Czech Republic can now be displayed as: