What you NEED to have LTE
To run LTE on a Device, you Need a LTE SIM, LTE Capable Device, LTE Plan, and a LTE Network.
You need those 4 things to be able to Have LTE on your device.
The 9900 or any new bb out right now will never suport LTE.
Even with the LTE SIM and LTE Plan, you will not get LTE Speeds becuase the 9900 handles only 14Mbps Speed. Where as LTE is 21 for my understanding.
So that being said, whether you do get a "LTE" Sim or stick with the one you got...you will only get max speeds of up to 14mpbs until a BB device is released that can go up to LTE Speeds.