This notation requires that international phone numbers include a leading plus sign (known as the ), and allows only spaces to separate groups of digits. EPP is a relatively recent protocol (finalized in 2004), designed for communication between domain name registries and registrars.
Because this version is written using free-spacing style, the literal space character has been replaced with ^ # Assert position at the beginning of the string. ITU-T Recommendation E.164 (“The international public telecommunication numbering plan”) can be downloaded at RFC 5733 defines the syntax and semantics of EPP contact identifiers, including international phone numbers. Techniques used in the regular expressions in this recipe are discussed in Chapter 2.
The rules and conventions used to print international phone numbers vary significantly around the world, so it’s hard to provide meaningful validation for an international phone number unless you adopt a strict format.
Fortunately, there is a simple, industry-standard notation specified by ITU-T E.123. This regular expression follows the international phone number notation specified by the Extensible Provisioning Protocol (EPP).
This data is passed to ASP script, or some other technology and if the data contains an error, there will be a delay before the information travels over the Internet to the server, is examined on the server, and then returns to the user along with an error message.
If you run a validation of the users form input before the form is submitted, there will be no wait time and redundant load on the server.
Otherwise it returns a message describing the error and highlight appropriate element with yellow.