When we first heard the rumour that Panasonic was going back into the phone business we didn't think it could be true. But, sure enough, at Photokina 2014 the Panasonic Lumix CM1 appeared.

Thing is, the CM1 isn't a phone. The clues are in the above sentence: Photokina is a camera show, and Lumix is Panasonic's camera brand and CM, supposedly, helps assert the device as a "communication camera".

So with a great deal of curiosity we went to see the Lumix CM1 to see what it was all about. After all, the only similar competitor - and not precisely similar - is Samsung, a company whose Galaxy Zoom and Galaxy Camera have surfed the divide between camera and phone with some compromises. Can Panasonic do any better?

We'll outline it by saying this: the CM1 impressed us a lot more than we thought it would. Yes it's thick by smartphone standards given its maximum 21mm depth - even the chunky Lumia 930 Windows Phone is 9.8mm - and heavy at 204g. But in camera terms the aluminium construction is thin and lightweight. Shame Panasonic has started to take cues from Samsung with that faux leather look though. Ugh.

Thing is, and almost contrary to our earlier statement, the CM1 isn't just a camera. It's a phone too. But more camera-phone than phone-camera. And with smartphone sizes ever on the increase - we snapped the CM1 next to our LG G3, which has a larger footprint - perhaps now makes more sense than ever for a device of this format to appear.

In addition to Android 4.4 running in the background, the Lumix CM1 has a dedicated "camera" switch that slides across (and pings back into position) to activate the camera in double-quick time.

You're then presented with an interface that's smartphone-like in essence, but can do a whole lot more. The 4.7-inch touchscreen is responsive and that 1920 x 1080 pixel LCD panel packs in plenty of detail.

The thickness in a landscape camera orientation suddenly makes more sense than a super-slim smartphone does, because holding this particular Lumix feels natural. The shutter button to the top (or side depending on how you look at it) is well positioned and falls naturally to the thumb, while the phone volume controls and on/off button are tucked further up this edge to keep them out of the way.

Surrounding the lens is a physical control ring - a first for a device such as this - that rotates to control the default setting in play. Whether that's aperture priority, shutter priority or another custom setting you want it to handle, the CM1 feels pretty decent in use.

But what the CM1 does that most other smartphones can't is deliver stacks of settings. Hit the virtual quick menu button and select all kinds of options: white balance, autofocus area, raw/JPEG shooting and so forth.

Full manual controls also feature, but you'll need a screen active with the red square visible in the top corner to switch between them. Press this and the virtual mode dial pops up, ready for your finger-based input. The front lens ring won't control this setting for some reason.

Then there's this realisation that Panasonic isn't mucking about with the CM1's specification. Under the hood there's a 1-inch sensor size - the same 20.2-megapixel chip as derived from the Lumix FZ1000, but in a body a lot smaller - that has its own Venus Engine to cater for the camera hardware and processing side of things.

That means the Android smartphone side of things is handled by a 2.3Ghz quad-core Qualcomm 801 chip set (MSM8974AB if you want the exact model) and, upon the flick of that "camera" switch, the Venus Engine kicks in. It means the camera functions don't require any of the smartphone's power to operate at all. Clever - but probably a costly implementation.

There's one slip-up in that arrangement that we saw, however, in that the camera can record 4K video… but only at 15fps. C'mon, use the Qualcomm to handle that and it would be a much higher frame rate.

Otherwise in use we found the Lumix CM1 to be really fast. The lens is a 28mm f/2.8 Leica-branded equivalent wide-angle, and although there's no optical zoom it is possible to pinch or click and drag to zoom in on the screen by up to four times (i.e. 4x for a 112mm maximum equivalent crop).

In a smartphone with a small sensor that might make for horrid jaggy edges, but the CM1 has a sensor so much larger - it's got more than two and a half times the diameter and over five and a half times the surface area of that of the Samsung Galaxy S5's sensor, for example - that the impact is reduced. However, we've not been able to take any sample images away.

The lens remains flush to the protruding lens ring when the camera is off, but can protrude for focus purposes when the camera is on. Not by a huge amount, but it's visible. However, that's not there to accommodate the zoom - which is what some may think.

Built-in to the CM1 are all the smartphone things you'd expect: you can make and take calls, connect to the internet via Wi-Fi and 4G LTE, there's Bluetooth and NFC, plus 16GB internal storage to ensure best installed app operation can be supplemented with microSD storage expansion.

The device did feel a little warm after some use though, and with just a 2600mAh battery and all that photo taking and sharing going on we don't imagine that will be the camera's strongest point. The battery can't be removed either, unlike some smartphone alternatives.

The Panasonic Lumix CM1 won't be coming to the UK at launch, presumably based on Panasonic's cautious approach to this new camera-phone (or is that phone-camera?) market. It's an interesting experiment though - and even if we wouldn't buy one to use as a dedicated phone, as a camera with direct sharing facilities (if, of course, you pay for the SIM and data) then there's a lot more going for the CM1 than we initially thought.

A guilty pleasure of Photokina? The Panasonic Lumix CM1 might well be just that. And we do love a rare surprise to pop up at these shows too.