'Symbian' is misspelt as 'Simbian' in moodlelib.php
This means that some phones that should be rejected are accepted as having qualifying user agents.
For example, with the user agent string for a Nokia N97:
Mozilla/5.0 (SymbianOS/9.4; Series60/5.0 NokiaN97-1/12.0.024; Profile/MIDP-2.1 Configuration/CLDC-1.1; en-us) AppleWebKit/525 (KHTML, like Gecko) BrowserNG/7.1.12344
check_browser_version('Safari') returns true. The expected behaviour is that it would return false, rejecting the phone due to the term 'SymbianOS' in the UA string.