Optimum Mobile leverages T-Mobile 4G LTE and 5G networks. T-Mobile has America\'s largest 5G network with more 5G bars in more places. Fastest: Based on median, overall combined 5G speeds according to analysis by Ookla^® of Speedtest Intelligence^® data 5G download speeds for Q4 2022. 5G capable device required; 5G not available in all areas.