Table schema:
CREATE TABLE table_19246_1 (carrier VARCHAR, frequency VARCHAR, launch_date__ddmmyyyy_ VARCHAR)

Question: When the launch date is 14.09.2005, and the frequency is 900mhz and 1800mhz, how many carriers are there?
SQL: SELECT COUNT(carrier) FROM table_19246_1 WHERE frequency = "900MHz and 1800MHz" AND launch_date__ddmmyyyy_ = "14.09.2005"