There could be multiple reasons. For starters, I'm not sure you would get 3G, because I'm assuming the free data is the slowest speed possible. That being said, and I could be wrong, the main difference you are seeing there I am assuming is because you are on different carriers. T-mo uses GSM technology for 2G, and there are two carriers in China that use GSM, China Mobile and China Unicom. My experience with the two generally has been that China Mobile has better signal everywhere. It's kinda like the AT&T and T-mobile of China. So a possible explanation would be that you are on China Mobile's network and she is on China Unicom, which would potentially explain the difference. Of course, it could also just be a coincidence that this happened. I have seen friends sit right beside me with an HTC One and get 4G while my LTE is running with full bars....
Phone: HTC One(M7)
Rom: Stock T-mobile 4.3
Your phone could benefit a lot if you quit trying to make it run like a IPhone.
We beat the hell out of an IPhone.
[New Members][Guide] Get the most out of XDA!!