AT&T Inc. (NYSE: T)'s first 5G mobile network is now online in 12 cities in the US.

As I reported on Tuesday (December 18), the network will initially be available in parts of 12 cities in the US. At first, AT&T is offering its Netgear Inc. (Nasdaq: NTGR) Nighthawk 5G hotspot, for free with 90 days of free data, but only for select businesses in the 5G coverage areas. (See AT&T's 5G Switches On in 12 US Cities, but Only for 'Early Adopters'.)

The hotspot won't be offered to the wider public til the spring of 2019. The price for the unit is a hefty $499, charging $70 for 15GB a month. The hotspot is intended to support up to 20 WiFi connections from the 5G device, although supporting so many connections is likely to put a hole in your data bucket pretty quickly.

AT&T told me that the device can "eventually reach a peak theoretical speed" up to 979 Mbit/s "in ideal lab conditions." Translation: Never gonna happen in the real world.