Then select More.
In the pop-up menu select Mobile Networks.
Since there are two SIM Cards in the handset, click on Select SIM Card option.
Choose the SIM Card you wish to use.
Then select Network Mode.
Click on WCDMA (preferred)/GSM option.
Select Network Operators If you wish to choose your network operator manually.
In the Service Provider pop-up menu, click on search networks.
In the pop-up menu choose the operator you wish (for instance if you live in Turkey, choose Turkcell with the most cost-effective tariffs).
After choosing the desired operator, go back to the Mobile Network Settings menu.
Check Data Enabled option in the pop-up menu.
Then activate Data Roaming.