Just know very little about the PHP, try without setting the encoding in XML declaration line (first line). WML 1.1 declaration on the second line should be OK for 7650 -- I tried with the following "headers" and got it work fine:
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.3//EN" "http://www.wapforum.org/DTD/wml13.dtd">
Have you configured/added text/vnd.wap.wml to you Apache web server as a MIME content type? It should be there by default, at least in the later ones of Apache releases.