How to check in which position (landscape or portrait) is the iPhone now?

Here are macros UIDeviceOrientationIsLandscape and UIDeviceOrientationIsPortrait

so rather checking separately you can do it like this ...

if (UIDeviceOrientationIsLandscape([UIDevice currentDevice].orientation))
{
    // code for landscape orientation      
}

OR

 if (UIDeviceOrientationIsPortrait([UIDevice currentDevice].orientation))
 {
     // code for Portrait orientation       
 }

As beno said, this seems a better answer if you are detecting orientation early in your View. I couldn't get the approved answer to return a result early in my setup but this works wonderfully.

if (UIDeviceOrientationIsPortrait(self.interfaceOrientation)){
//DO Portrait
}else{
//DO Landscape
}

Use the [[UIDevice currentDevice] orientation] method, as specified here.