Text and voice: complements, substitutes or both?

Text messaging has become an important revenue component for most mobile operators. We develop a simple model of demand for mobile services incorporating dynamics of information exchange. We show that when incoming communication stimulate outgoing communication, services that initially may be perceived as substitutes, such as mobile text and voice, may evolve into complements in terms of the price effect when the network size becomes large. We estimate the demand for text messaging in the Norwegian market and find that the cross-price effect of voice depends on the network size. Voice is a substitute for text messages for small network sizes, and a complement for large network sizes. Copyright 2009 The Author 2009. Published by Oxford University Press on behalf of Associazione ICC. All rights reserved., Oxford University Press.