This paper has been long forgotten from my memory among clutters of my hard disk. The paper is quite old but worthy of browsing, including its citations. Besides, the figure shown in the left clearly illustrates a schematic diagram of capacitive type multi-touch screen adopted in iPhone. Compare this drawing with Fig. 12 of Apple's patent multipoint touchscreen (US2006/0097991 A1).
DOI Link: S. Lee, W. Buxton, and K. C. Smith, "A multi-touch three dimensional touch-sensitive tablet," in CHI '85: Proceedings of the SIGCHI conference on Human factors in computing. New York, NY, USA, 1985, pp. 21--25.