Really glad I purchased this SIM. I will be living/working in mainland China for 6 months and purchased this SIM while I was still in the US. SIM arrived quickly and I quickly registered the number (email to the support as directed) popped it into one of only unlocked phones and it came up fine with no issues and even connected to AT&T, confirming that you can use the SIM while in the US but with expensive roaming.
Landed in China a few days later and turned the phone on. Took it less than 5 mins to connect to the network and was online before I got off the plane. I did have to set up the APN per the directions in order to get 4G data to work, but that was very easy to do as well with the directions. I have had the SIM for several days in China (Specifically in Shenzhen) and it has been working really well so far, with no issues. I will update as I go to other parts of mainland China and Hong Kong.
Had to call customer service once as I was having some issue with getting the texts to check my data and airtime balance. Customer service was very nice and was able to help quickly.
Perhaps there might be cheaper options as some other reviews mentioned but for me and my needs, this has worked very well even if at a slightly higher cost. Being able to purchase and activate it while in the US was a huge plus.
Very happy all around.

This SIM card worked well in Shanghai, China. Note that you will need to register it (not activate it) before you can use it due to Chinese law. You will get a detailed message how to email the registration information including a picture of your passport page. The registration process was quick. I got a confirmation in less than 24 hours.

You *should* read the user's manual from the LvyCom web site. The reason is that the instructions for international calling written on the slim teal booklet that comes with the SIM card are simply wrong. The booklet instructs you to dial 10193 001 to call a number in the USA from China. I followed these instructions and the call was dropped midway due to lack of funds. When I texted "2082" to "10010" get the balance, it showed that I did not use any of my 100 minutes. The mystery was solved once I read the user's manual. It states that you should dial 00 1 to call a number in the USA from China. This worked correctly, and my calls were accurately counted in my balance.

Another reason to read the user's manual is to decipher the response to balance inquiry text ("2082" to "10010"). The response is in Chinese. The user's manual explains where the balance can be found in the response.

I bought this and had one day delivery. It arrived the next day. I sent the passport photo and the phone number to the company to activate the SIM card. When I got to Shanghai Pudong (PVG), I had the China Unicom SIM in the phone, It required a couple of minutes after I turned it on to complete the connection. Once it did, I had data and voice before I got to the immigration queue. The calls to the US were free since I bought the package with 100 free minutes of calling. The data was great, since roaming data charges are ridiculously high.

I would definitely recommend buying this SIM card before going to China..

China Unicom uses GSM/HSDPA/LTE. My Samsung S6 Edge (Verizon) has all of these on the right channels and my phone is unlocked from Verizon. The LTE works like LTE in the US.

This SIM is pre-cut for all SIM card sizes. Pull your SIM card first to see what size you need, then separate the excess plastic using your fingers.

Tech Notes:
Unicom is the number 2 provider in China, but I use them because they are compatible with my phone since they use GSM.HSDPA/LTE. Their big competitor, China Mobile, uses TD-SCDMA which is only used in China. The iPhone 6S sold by Sprint and in the Apple stores includes TD-SCDMA and would work on China Mobile. My Samsung S6 does not. Furthermore, the other iPhone 6S models do not have TD-SCDMA capability.

The SIM is precut for the different size SIM cards used today. You simply punch out the size you need with your fingers. If you are uncertain which size your phone uses, remove your SIM card and compare it to the Unicom SIM card to see what you need to remove for it to fit.

I was immediately impressed with the company even before I bought the card. I asked a question (from the US), and it was answered fully within hours. Ordered and received the card. Yes, you do have to register the card (no burner phones allowed in China), you just have to follow the instructions. The company now provides a web link for submitting the information with a jpg of your passport. The website allows you to verify if the registration is successful, plus you get an e-mail. Inserted into a Moto G5 Plus on my way to China, and followed their CLEAR instructions for setting up the card for data. On arrival in China, it activated automatically, and it's working perfectly. Have used it to call the US, so much better than trying to use Skype or Magicjack with their inherent delays due to a slow internet. Data is working perfectly; use it with a witopia VPN, allowing use of google, google maps, etc. Several local calls made.

A PRC friend was a bit skeptical, and had offered to get me a China Unicom card in China, but this card is so much easier for the both of us. I had it on arrival, in case we didn't immediately meet up, and she does not have to cancel the card on my departure. It just works, with no hassles. The company follows up on your purchase, to make sure there are no problems, and responds quickly to any questions. Have bought this card 3 times now, and would DEFINITELY buy again from this company. This card is valid for 90 days, not the 15 or 30 days of other cards.

It works in China. You can call Chinese phones, Chinese phones can call you using a Chinese phone number, not an international number. It calls the US and just saved me when I had to spend 45 minutes with my bank when despite my travel notice, they locked my card due to "suspicious" activity. When outside wi-fi coverage, the data capability allows you to use the internet, though I'd get a VPN so you are not locked behind the Great Firewall. Don't believe the negative reviews, I am currently in China using it, and can verify it works IF you follow the CLEAR instructions for registration and setup. If you can fill in a simple web form and upload a jpg, you can register. Setting it up for data is clearly explained.

I bought the 2GB data plus 100 minutes talk time and only used half for my two week trip. I did take it easy on using my data at first, turning off data use on many apps. by the end of the trip I had turned it all back on and was using mobile internet like crazy, still only used about 100 MB per day. So I could have used the less expensive 1GB data plan easily. But if you don't want to have to worry at all about data, just buy the 4 GB cared.

This was my first time using a SIM card for a trip, and I will do this from now on when I travel, so much cheaper than buying the foreign roaming data plan through my phone company. If you have never used one before, like me, You just need to know a few things. First, the phone needs to be unlocked. If you have finished your two year contract for example, with ATT then they are required to let you unlock your phone. If it is paid off in full , then again they are required to let you unlock it. Just go to the phone company website to learn how to unlock your phone. Or buy an unlocked phone through the Apple store. Next, when you switch the card out, you can still use all your apps and everything is exactly the same except you just have a new phone number while you are in china. I powered down the phone and switched the cards while I was in the airplane to china, and then when I powered it back up it found a cell phone signal in China. 4G networks most places. Easy to use, much cheaper way to use my iPhone in a foreign country!