PHP mailing functionality is limited on free account to prevent abuse. To make it working, your mailing script should be configured to use SMTP server 'cpanel.freehosting.com' and to authenticate against it using credentials of email account set up in cpanel.
Paid accounts are provided with unrestricted access to PHP mailing functionality.
You can find more info on setting up email authentication in PHP scripts at this link:
http://email.about.com/od/emailprogrammingtips/qt/PHP_Email_SMTP_Authentication.htm
Optionally, PHP mail() can be enabled by purchasing corresponding addon HERE.
