Yeastar TG400L 4 Ports 4G LTE Gateway The Yeastar TG400L connects 4G LTE to VoIP networks to provide 2-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 soft switches to a 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 TG400L Key Features