From what I know file_get_contents() will only be able to fetch a remote file in PHP5. I'm not sure it ever worked in PHP4 or any version before that. The function that I wrote works for fetching any kind of external file and has worked successfully for me on every project I have required it for ever since I wrote it. I guess the only other thing I can suggest is what timvw suggested and use CURL.
file_get_contents() and its siblings have been able to fetch remote pages since at least PHP 4.0.3.. It appears to have been included in versions before it.