This paper examines whether the 'cross ownership' of wireline and wireless communications carriers is socially beneficial or harmful, and therefore should be allowed or regulated. We analyze a generic model of cross ownership of the firms which produce different but inter-related services. We show that, first, if both of the wireline and wireless industries are monopolistic, cross ownership results in social gains when the two services are complements, and social losses when they are substitutes. Secondly, if the wireless industry is sufficiently competitive, there's little or no welfare loss from cross ownership. Finally, we briefly address the effect of network externality on the welfare consequences of cross ownership. (C) 2003 Elsevier B.V. All rights reserved.