Many Tosibox products and accessories use SIM cards. Please use this reference to determine the correct SIM for your device:
Credit: Justin Ormont via Wikimedia Link
Tosibox Lock 175 Series - Mini SIM (2FF)
Tosibox Lock 500i Series - Micro SIM (3FF)
Tosibox Lock 600 Series - Mini SIM (2FF)
Tosibox Modem TB4GMx - Mini SIM (2FF)
MultiTech MTC Series - Mini SIM (2FF)
MultiTech MTR Series (MTR-@@@7) - Micro SIM (3FF)
MultiTech MTR Series (MTR-@@@1, MTR-@@@2) - Mini SIM (2FF)
Huawei MS Series - Mini SIM (2FF)
The SIM should be inserted into the Lock 500i with the metal contacts facing the green circuit board, and with the notched corner facing down, as shown:
Please see this article to obtain SIMs in North America: