Another development trend is the concept of core functions. PBX service has always been difficult for some small companies, because many companies believe that solving the problem of telephone is not the core function of the company itself. These considerations have led to the emergence of the concept of hosted PBX. For the installation of hosted PBX, PBX is installed at the telephone supplier and managed by the supplier. All functions and calls are transmitted through the Internet. What customers need is simply signing a service contract, rather than purchasing and maintaining expensive equipment.