SIM Full Form, What is SIM?

SIM full form Subscriber Identification Module.

The account holder is the subscriber. The cellular network uses the ID provided by the SIM to identify what phone number will be connected to a phone carrying that SIM card. The SIM card also identifies its issuing network, and when roaming in different countries, the foreign networks will use this identification to establish whether they will support the card or not. When roaming, the SIM will retain the phone number that is linked to it and will act as though it is in the country for its home network.

Move the SIM card to another phone, and that other phone will take over the phone number. This is subject to the new phone being compatible physically (there are different sizes of SIM card), and the phone is not blocked from working with the network used by the SIM.

How to port SIM:

If the subscriber moves to a different network, the new network will issue a replacement SIM. The phone number may be ported from the old SIM to the new one. Note: the old account must not be closed down before the number is transferred or the number may be lost. You should also note that the phone may be blocked from accepting a SIM from a different network. If necessary, the block can normally be removed although a charge may be payable for this service.