We have a device that collects data from vehicles. Currently the data is transferred to office with GSM modems. Some customers would like to avoid the costs involved to this option and have another wireless method to transfer the data. GPRS is not acceptable solution, there should not be any costs at all.
In this case the vehicles visit a terminal regualiry, so short/medium range wireless transfer solutions could be used. The range should be at least 1 km. 100 m is (probably) not enough.
The data transfer rate does not need to be high, 9600 bit/s is enough. Our device has a serial port (and limited amount of memory).
There can be many vehicles (100?) at the terminal at the same time, so there must be a way to address them separately. Only one vehicle needs to be addressed at a time. A master node (office) initiates the data transfer.
Cost matters, as always. All options are however worth investigating.