Wireless Mesh networking is a recent technology proposed to extend and improve the Wireless LAN capabilities to even larger geographical areas. Parallel advances in network-delivered services have created a situation where more and more end-users will want to use richer services based on the network. However, wireless networks have capacity bottlenecks due to reasons of their broadcast nature, MAC layer constraints among others. The paradigm of cross-layer design is especially relevant in wireless networks so as to effect key optimizations to improve performance. In this paper, we look at the specific service of Voiceover IP over Wireless Mesh Networks and quantify the capacity constraints using algebraic functions, fit to experimental(simulation) results. We use the Response Surface Methodology for this purpose. We also look at how application level parameters can be adapted to MAC level parameters so as to improve total call capacity, by use of our cross layer “metamodel.”