PBX Installation & Configuration

I'm in need of an experienced service provider to install and configure a PBX system with 25 extensions. The system I need is an on-premise one which does not require integration with CRM or any other software. I expect the service provider to be well versed in PBX installation and configuration and have experience with similar systems. The project requires all necessary supplies, installation, and configuration of the PBX system with 25 extensions. Upon completion of the job, I would like to be fully operational with the new system.