podes utilizar la funcion POPUP_GET_VALUES
DATA: BEGIN OF FIELDS OCCURS 1.
INCLUDE STRUCTURE SVAL.
DATA: END OF FIELDS,
RETURNCODE TYPE C.
FIELDS-TABNAME = 'SM04DIC'.
FIELDS-FIELDNAME = 'POPUPMSG'.
FIELDS-FIELDTEXT = 'Message :'.
CONCATENATE ' - Msg from' SY-UNAME '.' INTO FIELDS-VALUE SEPARATED
BY ' '.
APPEND FIELDS.
CALL FUNCTION 'POPUP_GET_VALUES'
EXPORTING POPUP_TITLE = 'Supply the popup message'
IMPORTING RETURNCODE = P_RETURNCODE
TABLES FIELDS = FIELDS.
IF P_RETURNCODE = 'A'.
EXIT.
ELSE.
READ TABLE FIELDS INDEX 1.
P_L_MSG = FIELDS-VALUE.
ENDIF.
espero te sirva
