This article applies to the CDMA/LTE version of the Samsung Galaxy Tab SCH-i905 and doesn't 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, tap Apps (located in the upper-right).
From the All tab, tap Settings.
Tap Wireless & networks.
Tap Mobile networks.
Tap Use Packet data to enable or disable.
Enabled when a check mark is present.