When I activate Joomla Mobile for the iPhone (this is the only mobile device I can check, so I am not sure if it happens on the other templates, but since it is a php server error I guess these templates have the same problem) I get the following warnings/errors. The menu and content is correctly shown underneath this warnings:

call-time pass-by-reference has been deprecated in c:....../modules/mod_mj_menu/mod_mj_menu.php on line 56
call-time pass-by-reference has been deprecated in c:....../modules/mod_mj_menu/mod_mj_menu.php on line 57

the lines it is refering to are:

$exclude_menu_ids = explode(',', $params->get('excludemenu'));
JMobileMenuHelper::prepareMenu(&$rows, $exclude_menu_ids, $params);
JMobileMenuHelper::prepareMenu(&$subrows, $exclude_menu_ids, $params);

Server:
PHP: php5 (5.2.17)
SQL: MySQL 5

removing the '&' before $rows and $subrows did remove the error, but I am not sure if this is the right solution

Yes, it's right.