I would like to know what do I need to have/do in order to star working on this. My main Idea is to use SDR (maybe USRP, maybe GNU Radio HW) to fake a BaseStation (transmitting in a high power, I guess) so all the cell phones within a small area would receive Broadcasted SMS. This is intended to be used in rescue labours and looking for missing people/children in crowded areas such as beaches, concerts, etc. ANY help or comments that you could give is going to be helpful. Thanks, so much thanks in advance.