Dual-SIM phones are not new, but until recently they were not good enough for both voice and data. The ZTE Axon 7 is the one that represents the new generation of dual-SIM phones.
An alternative is the Le S3 for about $150. It lacks some Verizon bands though and it cannot make calls with a Verizon SIM; LTE data only. The Mini version of the Axon 7 is very similar to the Le S3 on these regards; so is the Le Pro 3.
With such a dual-SIM phone, you can use the cheapest or best services for voice and data separately. For example, you can use a Tracfone or ExpoMobile SIM for very cheap and good voice calls on Verizon network while using a T-Mobile SIM for data. You may also use a Truephone SIM for free voice calls and text while using another SIM for data on T-Mobile, Verizon or AT&T. Such a dual-SIM phone is also extremely handy when you travel in another country including China.
Two big issues with Le S3