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. T-Mobile is America’s most awarded 5G network with the most individual awards for nationwide 5G metrics in public reports from independent industry experts. 5G capable device required; 5G not available in all areas.