The Yeastar TG200 connects GSM to VoIP networks to provide two-way communication: GSM/3G/4G to VoIP and VoIP to GSM/3G/4G. It allows you to connect most IP-based telephone systems including Yeastar IP Phone Systems, and softswitches to a GSM or 3G WCDMA or 4G LTE, which can provide a sophisticated fallback solution when landlines go down or be used to increase call traffic capacity by providing additional dial-tone.