This article applies to the CDMA/LTE version of the Samsung Galaxy Tab SCH-i905 and does not apply to the WiFi only version. A quick method to identify the device version is the location of the volume control keys.
From a home screen, select Apps (located in the upper right).
From the All tab, select Settings.
Select Wireless & networks.
Select Mobile networks.
Select Activate device.
Select Activate. Activation / PRL update may take a few moments.