The iPhone 4S will be provisioned automatically with the right settings upon first usage with the BASE SIM card. To request these settings again, connect your device to your PC and run iTunes to install the socalled ‘Carrier Settings’.
For instructions how to configure your iPhone 4S manually, choose Next.
Choose (Mobile) Network.
Choose Cellular Data, and enable this option.
Choose Cellular Data Network.
If Cellular Data Network is not available, manual configuration is not possible. In this case, connect the device to the computer, and use iTunes to install the ‘Carrier Settings’.
Edit your Cellular Data settings as follows:
Under APN, enter gprs.base.be (be aware of the dots).
Under Username, enter base.
Under Password, enter base.
Return to the Start screen.
Switch the iPhone 4S off and then on again to activate the settings.
You can now start using the internet. Click here for step-by-step instructions.