Category 4 LTE supports 150Mb/s download speeds and is already being implemented by other vendors.
This should give NVidia a better chance against its main competitors (in the Smartphone markets) Qualcomm, Broadcom and LTE-only specialist Altair.
NVidia gained LTE experience by acquiring UK company Icera which uses a software defined architecture and though this technology has been used alongside Tegra4 CPU devices as a separate package, the Tegra4i integrates the technology on to the system as the Tegra4. As Icera's technology is software defined, no actual hardware modifications were required to implement the enhancements.
Currently no mobile networks actually support Category-4 LTE (or LTE Advanced), though Japan's NTT Docomo has said they'll be announcing services by the end of the year.