Suggested research:
http://us.php.net/manual/en/function.explode.php
http://us3.php.net/manual/en/function.file-put-contents.php
edited to add:
http://us3.php.net/manual/en/function.file-get-contents.php
If you end up with a 3rd party service, don't pay Aweber. Go for MailChimp. They've got a free plan if your mailing list isn't that big.
