Wordpress检测用户电话类型

Is there any way to detect user phone type for wordpress??

I found some plugin but I would like to write the script myself.

Here is my situation. I need to change the web meta name viewport to

<meta name="viewport" content="width=320, minimal-ui">

when detect user is using iphone4 while load

<meta name="viewport" content="width=device-width, initial-scale=1.0">

during normal browsing.

Earlier, I found a method in wordpress to detect whether user is in mobile or not. But is there any method to detect the user phone type?