Push-To-Talk (PTT) is a simple communication service that allows a group of people to exchange voice messages. PTT is very popular among law enforcement agents and other emergency services. Its half-duplex nature and regulated operation helps users speak without interruption in an ordered fashion. Professional Mobile Radio (PMR) systems provide voice and data services to first responders and maintain PTT as their most used feature. Next generation PMR solutions are likely to converge with public land mobile technologies such as Long Term Evolution (LTE) to benefit from higher data rates and better interoperation with other existing networks. During catastrophic events, the supporting infrastructure networks could be destroyed, saturated or absent. Therefore, it is helpful to deploy temporary networks on the isolated areas and backhaul them by means of geostationary satellites to connect to the core backbone. In this thesis, we study the adaptation of the PTT application to this hybrid environment based on satellite links and LTE networks. Legacy solutions were designed without considering the satellite as a key part of the system. Hence, we take the opportunity of the PMR systems evolution to incorporate the challenges of the satellite framework.