When we have a SIM card associated with a number this card will contain this number, even if the phone used is changed or the SIM card is placed in another phone it will be the same number working on the phone. There is a difference between deactivated SIM cards and terminated SIM cards. The network provider can activate deactivated SIM cards under certain circumstances.
However, SIM cards are mainly designed to be activated for single use, if a SIM card is actively used for a long period of time it will just work fine but once the line is not in use for over 90 days or no chargeable activity is detected on the line associated with the SIM card, first the number become suspended then deactivated, but the SIM card is a technical item, if the owner takes the phone and the SIM card to the network providers retail unit they can activate the SIM card if it has not expired, in other terms terminated. In some cases, the SIM cards may need to be changed for even assigning the same number to be activated in a different SIM card.
SIM cards serve as a connector to the cellular network for mobile phones. The lifespan of SIM cards varies depending on the quality of manufacture, a good quality SIM card has a lifespan of up to 10 years. If the SIM card becomes faulty your device will have problems with low-quality voice connectivity, general functions will be restricted, and even the internet connection may get slower. In further scenarios, your phone will show signs as NO SIGNAL or INVALID SIM CARD. If this is your experience, then the SIM card needs to be changed and your number will be transferred to the new SIM.
Transferring an active mobile phone number to an old SIM card is more complicated than transferring it to a new SIM card and most network providers will prefer to supply a new SIM card where they can validate the quality and functionality of the SIM card. It is similar to changing a mechanical part of a car for a specific brand, although there is a replacement that is not produced by the brand owner, the brand owner company would suggest or guarantee any parts that are not their production. The same rules apply to network providers, they have access to the IT structure to activate or transfer a number to the SIM cards assigned to their company.
Although technically the SIM cards unexpired should be functional it is advisable to renew the SIM card to not have issues in the coming days.