Opel have not finalized the details of exactly what version of WiMax or frequencies they will use. They have indicated they are likely to choose 802.16d (aka 802.16-2004 or "fixed MiMax"). WiMax on the 5.4GHz or 5.8GHz spectrum under a class licence.
One way to make the networks stretch further would be to make use of the consumer installed equipment to relay the service to other consumers. There is work underway on 802.16j, mobile multi-hop relay (MMR) extensions to MiMax. This would allow a mesh, grid, or repeaters to route data through one or more customer units to extend the range of the network. Those standards are not ready, but Opel might choose a pre-standard implementation from one vendor.Also Opel could extend the reach of the network, by having WiFi hotspots on the consumer WiMax base stations, as Fon/BT are doing in the UK. This copuld be used to relay the service around a set of farm buildings, between small hobby farms or in a town. This could also be used with WiFi equipped smartphones, PDAs and cordless handsets, to provide a home phone service.