Can be found in iPhone SDK>Contents>iPhoneSDK.dist. Not sure how far back in the betas this goes but it's in Beta 6.
HTML:
function isgte106()
{
// 10.6 or above
if( system.compareVersions(my.target.systemVersion.ProductVersion, '10.6') >= 0 )
{
return true;
}
return false;
}