Why use curl instead of other methods?

I would like to know why it is better to use curl instead off other methods like $ret=file($url) in php. This is actually used to access an http api for an sms gateway.

Someone dropped a "I would recommend using curl for http connections", but I don't know why.

I just read that it is necessary for Paypal payments, so that does sound interesting.

I did a Google search "why use libcurl", but I haven't found an answer yet.

Could someone explain please?