Contents: Phone | Internet | WiFi phones | SIM cards

Phone:
You can use wifi calling if your phone is WiFi enabled for voice . All four major US carriers (T-Mobile, Sprint, AT&T and Verizon) provide built-in Wi-Fi calling , although the capability depends on the model of your phone and you may have to have it enabled.
See Everything you need to know about Wi-Fi calling - CNET,
What is Wi-Fi Calling and which devices support it? - Pocket-lint
and WiFi phones

WeChat is text messaging app popular in China. China's "App For Everything", with numerous unique functions and platforms ranging from 'payment' to 'social media' to 'services' to 'shopping' and more.
iOS (go to app store), Android

You can get a SIM card for your phone to allow local calling in China.
It is better to get it in the U.S. before you leave.
Your phone needs to be unlocked for the SIM card to work overseas.
Verizon does not lock their 4G LTE or 3G devices
See Device Unlocking Policy | Verizon
and SIM cards below
Also see TravelPass International Phones & Global Calling Plans | Verizon Wireless

You can enable International Roaming with AT&T Passport

WhatsApp is a texting service which works over the internet.

Using my Verizon iPhone5 while studying abroad in China. - China Forum - TripAdvisor - I am in college and am studying abroad in China from August-December 2014.
- I have a 16GB Verizon iPhone5.
- I want to be able to call and text back to US.
- A data plan of some sort would be nice (I could sacrifice the data if need be!)
- Verizon tells me it will be better for me to buy a sim card in China.
What exactly I want to know: - Are there different types of prepaid sim cards? (# of minutes/texts/data?)
- With a Chinese sim card will I be able to call or text back to the US or only locally?
- Do Chinese sim cards have limited life spans? I will be there for about 4.5 months.
- Does anyone have any experience with Wifi in China? Is there a lot of free Wifi spots?
- Does anyone have any experience with buying Chinese sim cards? (Cost/Difficulty)

Thanks so much in advance for any help or advice you can provide me!

Edited: 4:40 pm, February 10, 2014 _____________________________ Answers:
Sure you can do that and you can obviously call anywhere in the world although you should call using Skype, which is cheaper.

There are numerous plans. These are monthly plans, so you need to "re-load" the card with additional money every month. At the store where you buy the SIM they will show you the various plans. My plan is costing 98RMN per month and gives me 300mb of data which I find sufficient and more calls and SMS than I need.

In the summer of 2017 China's Ministry of Industry and Information Technology has confirmed that there is no ban on providing VPN services to individuals, and that media reports suggesting otherwise were inaccurate.

VPN	Cost	Countries	Comment
ExpressVPN	$12.90/mo	94	(Fastest for the US)
IPVANISH	$10.00/mo	100+	(Best for International)
vyprvpn	$5/mo	70

5 Best VPNs in China – VPNs.com vpns | Tom's Guide

A lot of restaurants and most coffee shops have free wifi.

Hacker News says, "Never use Google Maps in China; Google Maps in China are just hilariously wrong and out of date and will get you lost. Even if Google Maps wasn't blocked you wouldn't want use it in China. Apple Maps is the best English language solution, it's accurate and up to date; that or Baidu Maps if you read Chinese."

Internet in China, WiFi Availability | travelchinaguide.com

Verizon USA (website) - iPhone 6s/6s Plus, iPhone SE, Samsung Galaxy S7/S7 Edge, Galaxy S6/S6 Edge, Galaxy J3 V, HTC 10, BlackBerry PRIV, LG V20, LG G5, LG Stylo 2 V, Moto DROID Turbo 2.

AT&T USA (website) - iPhone 7/7 Plus, iPhone 6s/6s Plus, iPhone SE, Samsung Galaxy S7/S7 Edge/S7 Active, Galaxy S6 Edge, LG K10, LG V20, LG V10, LG G5.

T-Mobile USA (website) promised to enable Wi-Fi Calling for all its devices.

Sprint USA (website) - iPhone 5C, iPhone 5S, iPhone SE, iPhone 6/6 Plus, iPhone 6s/6s Plus, iPhone 7/7 Plus.

Source: What is Wi-Fi Calling and which devices support it? - Pocket-lint

Some that a Chinese friend recommended:
1. China Mobile 10-Day Data Prepaid SIM Card
Data only, no voice or SMS. Activation when arrived in China or Hong Kong.
$15 ebay | $19 Amazon

2. China, Hong Kong Unicom prepaid sim - Cross Border King 4G Voice, SMS and Data. Activation when arrived in China or Hong Kong.
Can access Gmail in China
$25 Amazon:
$25 1GB 4G LTE data + 50 mins local calls or 100 texts,! Free Incoming Calls and Texts
$40 2GB 4G data + 100 mins to US or Canada + 50 mins local calls or 100 texts,! Free incoming calls and texts!

3. Lvycom SIM card 1GB 4G LTE data + 50 mins local calls or 100 texts (on Amazon) ACTIVATION PROCESS: After you receive your SIM card, you MUST email: (1) passport information; (2) Amazon order ID; (3) Phone number on the SIM card holder. Detail instruction will be sent to you via Amazon messaging center once your make your order.
Amazon