(keitai-l) basic question about fees

Hi all, I am fairly new to the i-mode, having just recently puchased a
P502i.  I am a little unsure about the online charges while browsing.  I am
aware NTT charges by the amount of data transmitted.  What is this charge?

Also, my friend tells me that certain sites charge a flat fee, say 300 yen,
and when you use these sites you do not pay any of the data-metered fees NTT
would otherwise charge.  Is this true?

Roy