Sharp SH7228U always shows that there is not enough SMS memory. What should I do?

Turn off the phone first. It may be that some operators are out of memory because they accept short messages from problem cards ... and then set the storage location of short messages, preferably SIM cards. If the storage location is wrong, no matter how you save it, it will show that there is not enough memory. It also depends on whether there is MMS, which takes up a lot of space.