Do I have ROM in my phone? How can I find how much ROM I have? This is my phone, Samsung Galaxy S LCD I9003. Samsung Galaxy S I9000 has a ROM of 2 GB. What are the uses of ROM? I heard it is used to flash custom kernels. Cant I flash custom kernels in mine as nothing about ROM is mentioned?
Usually, Read-Only Memory is called internal storage, specifically the system partition on that storage (since other areas are writable by default). The image of the phone's firmware and OS is the ROM.  (That's how we do it on this site, anyways).

So your internal storage is 2 GB, and your phone's firmware and OS is installed on that storage space.  You can flash new kernels or entire ROMs (kernel + other firmware + OS) as long as they fit on the internal storage.  Generally, this isn't a problem; you won't find a ROM image for your phone that doesn't actually fit on your phone.