BlackBerry has released a new handset with some unusual features including a square screen and a touch-sensitive physical keyboard. It’s an attempt to recapture the business market but may serve as a test bed for the unusual physical aspects.

The BlackBerry Passport is so named because it’s roughly the same size as the passports used in most countries, albeit a bit thicker at just under a centimeter.

The Wall Street Journal noticed another handy size comparison: the screen is roughly the size of a slice of processed cheese, with a 1440 by 1440 pixel display. One reason for that is that makers Research In Motion believe it’s the best way to optimize screen space while keeping its traditional physical keyboard.

Another, according to RIM, is that the extra width makes it easier to read websites and documents (particularly letter-sized PDFs) without having to rotate the phone. That’s a clear sign that business users, who once saw the BlackBerry as the pocket e-mail machine, are at the heart of the device’s target audience; for those more likely to be watching videos, the shape is hardly ideal.

Early reviews suggest these benefits are useful, but it comes at the expense of the phone being difficult to hold in one hand.

With the keyboard, it appears RIM tried to get the best of both worlds and may have achieved neither. While it has a physical keyboard, you can use a swipe gesture over the keys for several commands: left to delete a word, down to scroll through the e-mail you are typing or reading, and up on the left, middle or right of the keyboard to choose one of three autocomplete suggestions.

The keyboard is a bit of a compromise: it’s only got three lines, covering letters. Numbers, punctuation and other symbols are only available through an on-screen virtual keypad.

The combination of typing on physical keys and using swipe gestures has had mixed reviews: the consensus seems to be that after a few weeks of adjustment you can type at a decent pace, though it’s unlikely to be an improvement over an old-school BlackBerry with an all-physical keyboard.

If the experience of WSJ’s Joanna Stern is anything to go by, the Passport is a great update to a mid-2000s BlackBerry, but the problem is that it’s not the mid-2000s any more and the idea of a phone that’s dedicated to and optimized for work use may no longer be relevant for many buyers.