As ssandy pointed out in greater detail, this is simply not going to do what you would like it to.

$telnet = `telnet $hostname `;
$telnet -> waitfor('/Username: $/i');
[download]

If you want to script a telnet session, `telnet` isn't going to get you there; you're going to have to find another approach (such as Net::Telnet).

Perhaps you might want to tell us more about why you decided NOT to use Net::Telnet. Perhaps someone here can help you get it to do what you need.