Can't an old computer send short messages without a memory card?

Memory cards have nothing to do with sending and receiving text messages and storing phone numbers.

Generally stored in the SIM card, that is, the calling card inserted in the mobile phone given by China Mobile or China Unicom or the telecom company when the number is opened.

This is especially true for the elderly, because the elderly can't choose or change the storage location of SMS phone numbers, and they can only store them on the default SIM card.