Roaming
Updated
Roaming is the use of a visited mobile network by a device whose subscription belongs to another network, its home network, under an agreement between the two operators. The rules that let a device use visited networks are set by 3GPP TS 22.011.
In practice
Most global IoT SIMs work by roaming: one SIM gets coverage in many countries, but each visited network sees a foreign SIM. That is fine for devices on the move and can be a problem where permanent roaming is restricted.