A dial plan establishes the expected number and pattern of digits for a telephone number, with E.164 defining the International standard. This includes country codes, access codes, area codes, and all combinations of digits dialed. For instance, the North American Public Switched Telephone Network (PSTN) uses a 10-digit dial plan based on the North American Numbering Plan (NANP) with the format of NPX-NXX-XXXX where N = 2-9, P = 0-8, and X = 0-9.Traditionally, organizations would create a private dial different from the E.164 standard for internal calling to:
* Reduce the number of digits to dial (shortcuts)--4-5 digits within the office, 5-7 digits between offices
* Call trunk selection--Dial 9 to get an outside line, Dial 8 to call between offices within the company, Dial 7 for international calls
* Integrating Adjuncts--Voice mail, announcements, and inter-PBX connectivity
As more companies adopt soft phones and UC applications where contacting someone involves clicking their name on the screen, the use and value of reducing the number of digits to dial goes away. Add to this cell phones which use the public network dial plan. Using the public dialing plan forces users to dial 7 digits for inter-office calling. For those who still manually dial, is dialing a few extra digits worth the effort to build, support, and educate new users on a private dial plan?
Companies can still create their own private number plans within the E.164 standard if there is legacy equipment in the environment, like older voice mail systems, that do not support a 10 digit dial plan. For example, a private internal 7 digit dial plan within a company could be defined as 10X-XXXX. Public vs. private network call routing decisions can be made based on the standard number dialing within the IP Telephony platform and users no longer need to make the distinction.
As voice systems move to IP/SIP and integrate with other applications to form Unified Communications solutions, voice is just another application within IT. This means that voice applications should use standard IT components such as DNS for addressing through the ENUM standard, LDAP directories for all user information, and common development and support systems.
As always, changing user behavior is a challenge. But in this case, the change of behavior should be easy since the user will be using their work phone just like they use their home and cell phone.
Private dial plans should fade away as companies move to all IP/SIP voice systems.
