Below the LTE USB modems and carriers that support them. Currently the carriers supported are AT&T and Verizon.
USB dongle to use is the AT&T Beam (AirCard 340U) - Supported by Vigor2926 Family; Vigor 2133 family
USB dongle to use Pantech 4G LTE UML290 - Supported by Vigor 2960; Vigor2926 Family; Vigor 2952 Family; Vigor 2133 family
For Verizon configure APN Name vzwinternet unless you are instructed differently from your carrier.
In most cases the only configuration needed is enabling the WAN USB as shown below
It is important to know that Draytek has also launched the Vigor 2926L model that comes with built in LTE modem for At&T in which a not so reliable USB dongle modem is not required, all you need to do is insert the SIM card.