When you set permalinks option other than default, the following code is already posted in .htaccess file.
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /callerdb/
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /callerdb/index.php [L]
</IfModule>
# END WordPress
But that doesn't help as you already know.
So, this will work when you set rewrite_module, this can be done by going to "fix permissions" if available in your cpanel or you may contact your host.