$re = '/[\w-]+\.(?<!com\.)somehost(?:\.[\w-]+)+/';
$str = '<endpoint address="https://subsite.somehost.com/someservice.svc" ...
contract="com.somehost.subsite.someservice.MyServiceSoap" />
<endpoint address="https://othersub.somehost.com/anotherservice.svc" ...
contract="com.somehost.othersub.anotherservice.MyOtherServiceSoap" />';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php