I just received my Oneplus 3t and it can only get 2g/3g/4g service. There probably aren't very many, if any at all, of these phones on the network. Do you think I have to call Koodo and have them input the IMEI of the phone into the system to get full LTE service?
Nope it will not make a difference.
Make sure that LTE is enabled in your wireless network settings if there isn't an LTE option then LTE either isn't available on the device which I'm sure it is or 4g is what they consider LTE and display it as such.