It will be some time before every device is equipped to handle 5G cellular service. The term ‘5G capability’ refers to a given device’s ability to handle this new generation of mobile technology. To begin, some carriers will provide 5G wireless capability by adding accessories to phones designed for 4G. This will allow users to enjoy enhanced 5G speed without sacrificing current 4G capability.

When mobile devices are fully 5G capable, they will operate primarily on 5G networks without requiring add-on accessories. These devices will enjoy the full range of benefits that 5G broadband is expected to provide. 

For more info:  5G characteristics
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