Can I take 1920x1080 pictures on my IPhone?

You could use Applications -> Preview -> Tools -> Adjust Size, on your Mac to resize the picture.

And I'm sure there are iPhone apps available via the iTunes App Store that can do that right o

Well, a 12 mp camera is capable of pictures larger than that, so I would say it could. You would need to use some photo editing software to set the photo to that size.