9. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of: receiving at the switching system a first symbol sequence included in the network numbering plan and including an extension number of the switching system; in response to the receipt of the first symbol sequence, parsing the received first symbol sequence by using stored first information defining a syntax and a grammar of the network numbering plan and defining the first symbol sequence as a feature access code for a feature of the switching system, to determine a meaning of the first symbol sequence within the network numbering plan; and in response to the determined meaning of the received first symbol sequence, invoking said feature in the switching system.
10. The method of claim 9 further comprising the steps of receiving at the switching system, from a user directly served by the switching system, a second symbol sequence included in the internal numbering plan, and in response to the receipt of the second symbol sequence, parsing the received second symbol sequence by using stored second information defining a syntax and a grammar of the internal numbering plan and defining the second symbol sequence as a feature access code for a corresponding feature, to determine a meaning of the second symbol sequence within the internal numbering plan; wherein the stored first information defines the first symbol sequence as an equivalent of the second symbol sequence, and the step of invoking comprises the step of in response to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence, invoking the feature that corresponds to the second symbol sequence.