There are strong arguments about the positive effect of information and communication technologies (ICTs) on companies’ performance. This effect is also extensive for micro and small enterprises (MSEs), which tend to adopt ICTs in lower levels in comparison with large companies. In this context, this paper has two goals: to analyze the effect of firms’ size on (a) the relationship between strategic planning and ICTs use; (b) the relationship between ICTs use and interaction with customers. The sample of the study comprises 171 Brazilian MSEs, and we used confirmatory factor analysis and structural equation modeling to test our hypotheses. The main results indicated that even in small companies, size is an important variable to explain the antecedents and consequents of ICTs use. The positive effect of ICTs use was stronger among small companies, reinforcing the relevance of technology for them.