Yeastar offers a variety of modules and accessories to enhance the functionality of their IP PBX systems. Key modules include expansion modules like the EXP100, which add programmable keys for efficient communication, and SIP trunk modules for seamless VoIP integration. Yeastar also provides analog and digital trunk modules for connecting traditional phone systems and VoIP gateways for hybrid setups. Accessories include Yeastar IP phones, power supplies, cables, and rack mount kits for easy installation. These modules and accessories allow businesses to customize and expand their Yeastar PBX systems, ensuring optimal performance and scalability for communication needs.