I just figure this out, thanks for Google’s help. 
If you want to have fake sub-domain, which do nothing but to send request to your PHP script, so you don’t need to use separate script for each sub-domain, then this might be the simplest way to do. Yup, as easy as 1, 2, and 3……. lol
Okay, so this is how:
1. Create a sub-domain and fill the name with single “*” (without quotes). For example *.mydomain.com. Specify your sub-domain directory if you want, I use “sub”, so when there is (unknown) sub-domain called, it will automatically call the script in mydomain.com/sub.
2. Then add this piece of code to retrieve the sub-domain name.
$subdomain = preg_replace(“/^([\w-]+)\..*$/”, “\\1″, $_SERVER['HTTP_HOST']);
3. Done!!! Now you can process your script easily when you know the sub-domain.
i think this is a good article.. but dunno what function of it..
bro,, you have trick to ride off the file size limitations on some server??
happy blogging
The function is, for example when you want to provide a feature to create fake sub-domain for your user. In real work example, user would like to have sub-domain such as user.domain.com, which show the user profile page, this can be done easily with fake sub-domain, using a single script to process the request…
hmm… for file size limitation, I’m not sure, but you can try to ask your hosting or split the file…