2. For the specific standards supported by mobile phones, you need to contact mobile phone customer service or consult the mobile phone manual;
3. Unicom's 4G will automatically be backward compatible with 3G. If there is no 4G network in the location, it will automatically switch to 3G network; Unicom's 3G is automatically backward compatible with 2G, and it will automatically switch to 2G when there is no 3G signal or the 3G signal is unstable.