5. The arrangement of claim 3 wherein: the defining means further define the network numbering plan such that the symbol strings of individual types have variable lengths in terms of numbers of symbols that make up individual symbol strings of the individual type.
5. The arrangement of claim 3 wherein: the defining means further define the network numbering plan such that the symbol strings of individual types have variable lengths in terms of numbers of symbols that make up individual symbol strings of the individual type. 7. The arrangement of claim 5 wherein: the defining means comprise means for storing definitions of individual symbol strings of the network numbering plan, each definition including an identification of the string type of the defined string.