1. A method of recognising a numeric or alphanumeric sequence of characters in a document, said sequence conforming to predetermined rules, and representing user identifiers for identifying users in a communications system, the method comprising: identifying a country of origin of the document, the determined country of origin capable of being changed by a user; recalling rules relating to a format of said sequence associated with the determined country of origin; searching the document to identify any sequence in the document satisfying said format; determining a rate associated with said sequence; converting said sequence into a call format for the determined country of origin; and returning any such sequence and the determined rate in a currency associated with the determined country of origin.