In the latest version we have added a warning sign on the general settings page for the domain. This is for a reason. Telling the PBX how to interpret numbers makes it a lot easier to deal with the various ways to represent numbers in the different parts of the world.

Essentially there are two areas. The so-called NANPA region is essentially USA and Canada. NANPA stands for North American Number Plan Association. The organization deals with the distribution of the 10-digit number block allocated for the area. The area has the international dial code “1”. Usually numbers have exactly 10 digits, and they are commonly written in xxx-xxx-xxxx or (xxx) xxx-xxxx notation. In the old days when most calls were local, people could call just the 7 last digits and leave out the area code. This is why the area code was written in brackets. However today practically all calls include the area code. There are some numbers like 911, 411 or 555-xxxx which are an exception to the 10-digits rule. Because the number length in the NANPA region is predictable, it is possible to provision phones with a phone dial plan that automatically starts dialing when the number is complete. In that case users have to start dialing with a “1” when they want to call a 10-digit number.

The rest of the world is using numbers where the PBX is not able to predict how long the numbers are. In those areas the challenge is to guess how the number begins. Depending on the context, numbers may start with the country code, with the area code or just the local number. If the PBX has the country code and the area code, it can automatically convert numbers into the globally routable number. For example if the call comes in on trunk A through a local PSTN gateway, it will be able to call that number back through another trunk B.

In order to tell if a number is in a global format, the number must start with a plus sign. Users may even enter numbers starting with a plus sign to tell the PBX that no matter what the country code is, where to send the call. This has also become a common feature of many cell phones, especially in countries that have a lot of international calls. If users are entering numbers in the PBX starting with a plus sign, the PBX will happily accept it.

Otherwise, it is important that the PBX knows which country the number is in. That’s why we encourage everybody to check what country code has been set on the domain.

In the light of this discussion it becomes clear why putting a “9” in front of every number is a bad idea. In the old times when PBX were connected through analog lines (one cable for every possible phone call), this number was used to grab one of those lines and get the dial tone. However in today’s digital world and with the modern requirements such seizing of lines is not needed and looking at multiple trunks in a domain, even impossible. For example, when users dial 911 to call the emergency service, it seems ridiculous that they have to dial 9, wait for a dial tone and then dial 911. Most of the users have cell phones today. Fortunately this educates users that they can first enter and edit the number and then press the send button to start the call. There is no reason why they should not do the same thing on the VoIP phone.