Full firmware often wipes ISP-specific VOIP configurations. Ensure you have your SIP server details and passwords saved before upgrading. Where to Download?
Search for the specific hardware revision printed on the bottom of your ONT. firmware gm219s xpon full
Sites like 4PDA or OpenWrt forums often have community-verified universal dumps. Full firmware often wipes ISP-specific VOIP configurations
(e.g., Huawei, ZTE, Fiberhome).