I am implementing one phonegap application. here everything going fine but when i am talking device specifications like

1)BlackBerry Bold Touch 9900 Screen specifications are as following

Body    Dimensions  115 x 66 x 10.5 mm (4.53 x 2.60 x 0.41 in)
Weight              130 g (4.59 oz)
Keyboard QWERTY     Display     Type    TFT capacitive touchscreen, 16M colors
Size               640 x 480 pixels, 2.8 inches (~286 ppi pixel density)

But when i test following function in java script

function findScreenSize()
{
    alert("width:"+window.innerWidth +"Height:"+ window.innerHeight);   
}

it displaying SIZE width : 356 Height : 267 (356 x 267)

2)BlackBerry Bold Touch 9930 Screen specifications are as following

Body Dimensions     115 x 66 x 10.5 mm (4.53 x 2.60 x 0.41 in)
Weight          130 g (4.59 oz)
Keyboard QWERTY     - Touch-sensitive controls
Display     Type        TFT capacitive touchscreen, 16M colors
Size                640 x 480 pixels, 2.8 inches (~286 ppi pixel density)

then i run same javaScript function i got following output

it displaying SIZE width : 417 Height : 313 (417 x 313)

why it is behaving like this ?

Can anybody know relation between core pixel and HTML pixel please give answer