On regex string add /i for case insensitive or /s for case sensitive.
For example:
[php]
$regex_match = "/(iPhone|iPod|BlackBerry|Palm|Googlebot-Mobile|mobile|mobi|Windows Mobile|Safari Mobile|Mobile Safari|Android|Opera Mini)/s";
[/php]
and for case insensitive:
[php]
$regex_match = "/(ipad|android|android 3.0|xoom|sch-i800|playbook|tablet|kindle|Safari)/i";
[/php]
Hope it helps!