It might be easier to simply activate roaming on your Chinese sim. For both Mobile and Unicom, only a two minute phone phone call is required. Note that if you are not in your sim's home city/province, you might need to prepend with a city code in order to reach the right customer service center. And, assuming your sim is pre paid, you may need to top it up to around ~200. Customer service will give you specific instructions on this. Roaming in HK/Macau is honestly pretty cheap if you don't go crazy with calls or data usage.