The server will reply to all User Service requests with an XML result page. If the request was processed successfully the return will be a "result" element with a text body of "OK". If the request was unsuccessful, the return will be an "error" element with a text body of one of the following error strings.
The output is an XML file, so what you're looking at is using an XML parser to get the result element. simplexml will load it into an array (since this xml page is small you shouldn't have to worry about performance so more complicated xml parsers aren't worth the trouble)
$output = simplexml_load_string($odpoved)
switch($output->result) //check $odpoved to make sure the XML structure matches
Or, you can also pass the url using simplexml_load_file the output will be the same.
for more information, see: http://www.sitepoint.com/parsing-xml-with-simplexml/