The evolution of mobile communications systems leading to technologies like 4G-LTE is expected to substantiate high bandwidth applications, seamlessly. The necessity to connect the switches and gateways of these systems through microwave backhaul links to serve remote locations is inevitable. These links are not 100% reliable since the transmission path may be disconnected due to bad weather or equipment failures. Taking this premise as our starting point, in this paper, we propose a novel solution for increasing availability and reducing network costs of 4G-LTE mobile networks. This new concept that we have termed as Resiliency, Reliability, Redundancy by Infrastructure Sharing (3RIS) provides a solution to improve availability without additional cost investments, by sharing another operator's microwave backhaul. A proof of concept for the proposed solution has been evaluated by an analytical model that has been developed to show the advantages of infrastructure sharing.