Millimeter wave signals also drop off faster with distance than lower-frequency signals do, and the massive amount of data they transfer will require more connections to the landline internet. So cellular providers will have to install more, smaller, lower-power base stations rather than use existing powerful macrocells to offer the multi-gigabit speeds that millimeter wave networks promise.

5G home internet is also much easier for carriers to roll out than house-by-house fiber optic lines. Rather than digging up every street, carriers just have to install fiber optics to a cell site every few blocks, and then give customers wireless modems. Verizon chief network officer Nicki Palmer said the home internet service would eventually be offered wherever Verizon has 5G wireless, which will give it much broader coverage than the carrier's fiber-optic FiOS service.

The first round of 5G phones will only support some of the 5G systems being used in the US. They will not support low-band, FDD networks, such as T-Mobile's 600MHz and AT&T's old 3G spectrum. So if broad 5G coverage is more important to you than top speeds in urban areas, you may want to wait for phones that support those networks during the second half of the year.

Samsung has pledged an early flagship phone, probably the Samsung Galaxy S10, for AT&T, Verizon, and possibly Sprint. This will probably be announced in February and become available in March. The company has also said it will release a second 5G phone for AT&T's broader low-band network during the second half of the year.

Sprint has said an integrated 4G/5G Android phone from LG will come to its network during the "first half of 2019."

Verizon's first 5G phone could be the existing Moto Z3, which has a 5G add-on promised for early next year.