What is the make and model of your modem? As sfx2000 said, Cradlepoint does a pretty good job. I believe the MBR95 is the kind of device you need. Here's a list of supported modems:
AT&T
USB
Huawei E368 [Force 4G]
LG AD600 [USB Connect Adrenaline (LTE)]
LG Turbo LUU-2100TI [USBConnect Turbo]
Sierra Wireless AirCard USB 308 [Shockwave]
Sierra Wireless AirCard 313U [USB Connect Momentum 4G (LTE)]
Bell Mobility (CA)
USB
Novatel Wireless U679
Sierra Wireless 330U
POTS (Analog)
USB
Portsmith PSA1U1M
Rogers (CA)
USB
Sierra Wireless 330U [LTE Rocket Stick]
ZTE MF636 [ZTE MF636 Rocket Stick]
Sprint
USB
Franklin Wireless U770 [Plug-in-Connect Tri-Mode USB]
Franklin Wireless U600
NETGEAR 341U
Sierra Wireless AirCard USB 598 [Sprint 598U]
T-Mobile (USA)
USB
ZTE MF691 [webConnect Rocket 2.0 HSPA+]
ZTE MF683 [Rocket 3.0]
Verizon
USB
LG VL600 [VL600 4G LTE USB Modem]
Novatel Wireless Ovation MC551 [ 551L 4G LTE USB Modem]