Trouble connecting to remote SQL Server 2005 with PHP using mssql

I've been struggling with this for a ridiculous amount of time and I'm not sure what to do. I'm using PHP 5.4 on a GoDaddy Linux shared hosting account with the mssql module enabled. The database I'm trying to reach is hosted elsewhere. I'm trying to connect via mssql_connect. I've tried

$con = mssql_connect('<ip address>', 'user', 'pass');

as well as

$con = mssql_connect('<ip address>\<instance name>', 'user', 'pass');

And the above two with port numbers. But I still get the "Unable to connect to server" error. I've made sure SQL Server is accepting outside connections and SQL Agent is running. I can't use PDO with sqlserv because of GoDaddy, mssql is the only module I'm able to use.

Does anyone have any ideas as to what could be wrong?