Is your USB flash drive formatted as FAT or FAT32? It won't work with NTFS formatted drives. And what make and model is your USB 3G/4G modem? It should support certain Huawei and ZTE modems, like the Huawei E220 and 1750. It should state in the tablet's instructions, as to what is and isn't supported.
The People's Guide
to Android in the People's Republic.
Honorary Grand Poobah Shenzhen University English Corner.
There are nine million bicycles in Beijing.
There are nine million Androids in Shenzhen.