If you buy a China phone from internet, and has problem with your SIM card 3G data service, then setup it follow this guide.
This setting is only for Android phone with these condition:
1. MTK processor, including MT6573, MT6575, MT6577, MT6588, MT6599;
2. GSM network SIM card with 3G data service;
Setting > Wireless & networks > Mobile networks
1) 3G service > enable, Network Mode: GSM/WCDMA (auto mode)
2) Access Point Names (APN), press menu key, then add New APN, fill out the parameters.
Please inquire your SIM carrier about all parameters, or search it on internet, if you are not familiar with it.
Save and exit, then enjoy internet.