Found this in the ATIV S registry.
http://wap.samsungmobile.com/uaprof/GT-I8750.xml
It mentions LTE under supported bearers. But this is for the GT-I8750, not the SGH-T899M, which has LTE.
Very confusing. The ATIV S has an LTE chipset (My ATIV S' drivers are all MSM8960), but is LTE disabled by Samsung to cut costs by just using one motherboard and disabling LTE on one and enabling LTE on another?
WindowsPhone.com mentions that the GT-I8750 uses a MSM8960 chipset (LTE chipset), and I sincerely doubt that windowsphone.com would get the chipset wrong for a phone with its OS.
Conclusion: Samsung uses the same motherboard on both the SGH-T899M an GT-I8750 to cut costs and on the T899M, they flashed ROMs with LTE enabled and on the I8750, they flashed ROMs with LTE disabled. Similar to the Lumia 810, LTE can be disabled even though it has an LTE chipset. Kinda expected this from Samsung...