exec 5<>"/dev/tcp/localhost/80"
    echo -ne "GET / HTTP/1.1\r\nHost: localhost\r\n\r\n" > &5
    cat < &5

FTFY

/dev/tcp is a bashism. It's not a real (kernel-provided) device.

Clever, though nc really is better than telnet. It is much easier to pipe into just for starters.

Actually, you broke it. telnet sends CRLF line breaks like you're supposed to. nc will just send LF. A strict web server won't talk to you.