1. Future Trends in Telecommunications;Horrocks,1993
2. Voice Information Systems;Walters Robert,1991
3. Overview of the Audiotex PRS Market 1987–1992;Commission of the European Communities, Information Market Observatory;IMO Working Paper 93/3 final,1993
4. Santucci op cit Ref 11, 19
5. Ibid 15–16