How to make cell phone calls with the T-Mobile plan in Beijing China

I joined the T-Mobile’s Unlimited 55+ plan in US. I am going to China for two weeks. If I am in Beijing and want to call my friend’s Chinese Cell phone, do I need to dial 086 (China’s country code) + my friend’s Chinese 11-digit cell phone number? How can my friend in Beijing call me with her Chinese
cell phone? Does she need to call the 001 (US country code) + my 8 digit celll phone number? Can someone with the T-Mobile plans (T-Mobile one, T-Mobile 55+) who had traveled to Beijing share their experience?