Nvidia just showed the external LTE part of Tegra 4 and it calls it the i500 Soft Modem. This is the new LTE 4G programmable chip that is roughly 40 percent smaller than conventional LTE chips. It has 8 processors that can calculate 1.2 trillion operations per second and apparently, or according to Nvidia, does a pretty good job for a 4G modem. 

It is sampling now and it should be capable of supporting multiple bands due to its programmability.