A Grandstream GSM Gateway is a device that bridges VoIP systems with GSM cellular networks, allowing seamless communication between traditional telephony and mobile networks. It supports multiple SIM cards, high-quality voice codecs, and integrates easily with PBX systems, making it ideal for businesses seeking cost-effective and reliable connectivity. Regarding compatibility, these gateways are designed to work with most GSM, 3G, and 4G networks worldwide. Its compatibility depends on supported frequencies, regional network bands, & carrier-specific configurations.