Owing to the rapid progress in submicron CMOS technology analog/RF circuitry, memory can be integrated into the same chip together with the digital circuitry. However, such an integration scenario also means extra costs for mixed signal isolation and technology fusion. In this paper, we analyze cost and performance trade-offs for mixed-signal integration in system-on-chip through case studies of wireless system integration. It is shown that, depending on system complexity, integration scale, and mixed-signal performance requirements, single chip integration is not necessarily better for some systems in term of implementation cost. The analysis method emphasizes a priori estimation, and hence is useful for addressing implementation issues at early conceptual-level design phases.