Hybrid architectures including satellites are of undoubted interest for wireless networks deployment in rural and remote areas. We focus on VoIP capacity service optimization over a hybrid network and we compare performance under temperate and tropical propagation conditions. We have chosen a (GEO) satellite and wireless network combination, based on DVB-S2/RCS and WiMAX standards. This combination has already proven to be a relatively simple hybrid combination with enormous potential at both the service and architecture levels. In order to tackle the design of the hybrid network on a difficult propagation/topographical environment, we propose a cross-layer design across both layers and networks. Our proposal is based on commercially available VoIP codecs, and the cross-layer design does not require breaking the protocol stacks of both networks. We propose a centralized scenario where VoIP load control is performed through a physical-transport-application cross-layer information flow (inherently cross-layer across both networks). In particular, VoIP rate is centrally controlled in order to match the satellite link capacity drops due to physical layer adaptation to channel conditions. Realistic modeling is considered for both the hybrid architecture and the channels. We present numerical results of the proposed design showing that our cross-layer load control technique is able to maintain the active WiMAX number of connections for a wide range of rain attenuation in both temperate and tropical areas. © 2008 IEEE.