Data-only SIM cards (4G)

Has anyone tried these in their phones? They're SIM cards, but no voice nor SMS, just 4G data. Which you would normally use with a laptop or tablet to get the internet, but with the advent of messaging services like wechat where you can do voice and messaging over the internet....

As a replacement for regular phone services, these things have substantial disadvantages, like no phone calls from or with people you don't know, and maybe some other stuff, but it kinda seems like it could be cheaper than spending monthly money on a phone number I never use....

So, anyone used them before?

I'm getting conflicting accounts. On the one hand, China Unicom is introducing 4G, offering "value packs", and deprecating their 3G packages. On the other, the website says no 4G cards available in this area. Plus I've been thinking about it: the idea of the card is to make contact possible when I'm out of wifi range, and maybe 3G would be enough. 3G is reputedly "not good" for voip, but it'd be fine for text. My journeys in G start tomorrow when I go visit the local unicorn.

Well networking fans, several region and locale issues were encountered. In my area, data-only SIMs were discovered to be unavailable in person. And though they could be purchased online at China Unicom, they were offering only certain types, and not the one that would have suited my requirements (5Gb of 3g data for one year). Inasmuch as the SIM I could have bought offered way too much data per month and cost a lot more than I'd hoped, I caved and bought a phone number instead. 18 yuan per month for calls, SMS, and 2GB of 4g data. On my phone that means LTE.

Bonus news: China Unicom accepted my passport as a valid ID document in the purchase of this phone number.

Why care? Because for various reasons, I had earlier tried a last ditch attempt at resurrecting my China Mobile number. Their office once again lost their shit when confronted with only a passport. They wanted a Chinese ID card or get the hell away and go to the head office. Maybe head office can handle passports now but screw that, I'm with the unicorn now.