The Yeastar TG400W connects GSM or WCDMA or 4G LTE to VoIP networks to provide two-way communication: GSM/3G/4G to VoIP and VoIP to GSM/3G/4G. This 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. Yeastar TG400W Key Features GSM Voice Calls VoLTE for HD Calls Maximum Cost Reduction Top Quality and Reliability Mobile Connectivity for SMB