Best call option when overseas?

I'll be going to china soon, and it'll just be me and my mom. We both have smart phones (I have an iPhone 5 and she has an android one)
I can't speak Chinese well, so if I get lost, I'm SOL. Thus, I would like to have minutes on my phone to call my mom when I'm lost. I would say VOIP is a good option but Wi-Fi hotspots aren't always a guarantee.

What are my options in terms of call availability when overseas? My mom and I have T-mobile. The only things I know about are prepaid SIM cards or VOIP, but I hear that tmobile works overseas, but I can't imagine that option to be very cheap.

Buy cheap cell phones (You can get very basic ones for 160 yuan at a local Sunning store in China.) and get a local SIM card. (160 yuan is about 25 dollars.) You pay as you go. Very easy and much cheaper than paying international roaming fees.

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