如果你发送一条短信后回复信息 +CNTI：“SM”，3 这个3表示的是你现在这个卡上的第三条信息
此时发送AT+CMGR=3就可以读取这一条短信
如果要删除这一条短信的话发送AT+CMGD=3
下面是一些AT+CMGD指令的作用
AT+CMGD=1，0 The message from the preferred message storage at the location 1 is deleted
AT+CMGD=1，1 ALL READ messages from the preferred message storage are deleted
AT+CMGD=1，2 ALL READ messages and SENT mobile originated messages are deleted
AT+CMGD=1，3 ALL READ,SENT and UNSENT messages are deleted
AT+CMGD=1，4 ALL messages are deleted (删除所有短信)