Verizon & Korea are building. NTT DOCOMO & China Mobile close. Many others mostly holding back, doing little until 2021-2023.
2019 for mobile phones, Qualcomm promises, as TSMC ramps 7 nm process to produce the chips.
Latency will be 5-10 milliseconds to the cloud controller intelligence.
1-2 milliseconds will be measured from the tower to the phone, but that's meaningless until and unless intelligence moves to the edge. That's likely very rare for a decade because there's no apparent market for 1 ms. Most "use cases" are bogus according to experts in connected cars, virtual reality, and telemedicine. Gerhard Fettweis's Tactile Internet is inspiring but years or decades away most places.
Everything is 12-24 months ahead of what the most respected experts thought just a year ago. Verizon has deployed hundreds of prestandard cells, going to thousands. They are moving forward and are spending billions on fiber for backhaul.
Most telcos are doing more political pr than actual building. Almost all have more capacity than they can sell so see no reason to invest. DT CTO Bruno Jacobfeuburn says mmWave investing today is based on faith, not rational analysis.
Ericsson, Huawei, Nokia, Samsung, and ZTE are the choices. Ericsson, Huawei and Nokia have impressive public demonstrations. ZTE is respected by the Chinese telcos and more advanced than Westerners usually notice. Samsung has impressed Verizon.
I don't have enough information to know who is ahead.