The Vivo X3
The Vivo X3 is just a sliver thicker than the Gionee Elife S7 and S5.5 at 5.57mm. That said, it is not in the same ballpark as the all the above phones as it has a 5-inch 720p screen and an old Cortex A7 octa-core processor. It even skims on RAM as there's only 1GB on tap along with 16GB of internal storage. On the back, there's also a 13-megapixel camera. In the larger scheme of things it is not the greatest solution as it is stuck on Android 4.1 Jelly bean, which was launched way back in 2012.
Gionee Elife S7
With the new Gionee Elife S7, the Chinese smartphone vendor is actually scaling back its ambitions for an ultra slim phone. After the Elife S5.1, it has launched the Elife S7, which is actually slightly thicker at 5.5mm. This, however, comes with a number of benefits. You get a vibrant 5.2-inch FullHD screen, a fast 64-bit MediaTek octa-core processor, 2GB RAM, and 16GB of internal storage. It also has a nice 13-megapixel camera on the back and a 8-megapixel camera on the front. All this packaged in a uniquely designed phone running the latest version of Android in concert with Gionee's Amigo UI.
Gionee Elife S5.5
Back in early 2014, a phone measuring just 5.5mm was just unheard of. Then the Gionee ELife S5.5 came in the market. And boy, it was a gorgeous phone. In fact, it is still a formidable option. The phone uses a gorgeous 5-inch 1080p AMOLED display, 2GB RAM and an octa-core processor. It even has a 13-megapixel camera on the back. The phone made its way in to the Guinness Book of world records. How many phones can claim to achieve that?
Gionee Elife S5.1
Before Vivo and Oppo made their slim gambits, it was actually Gionee that held the crown of the slimmest phone in the world. In fact, it held the crown of the slimmest phone in the world for quite some time. The Elife S5.1 succeeded the Elife S5.5 as the slimmest phone in the world, but it came with some tradeoffs. Gionee had to downgrade the specifications of the device to reach the size zero. This resulted in an underclocked octa-core processor, lower resolution display, 2GB RAM and a lower resolution 8-megapixel camera on the back. That said the phone is a beauty.
Oppo R5
Like the Vivo X5 Max, the Oppo R5 packs similar hardware. It has the same processor and RAM, though a smaller 5.2-inch 1080p AMOLED display. The design of the device also looks starkly similar to what you'd get on the Vivo X5 Max. It is also slightly thicker than the X5 Max at 4.85mm. Unfortunately, due to the smaller form, it packs in only a 2,000 mAh battery. It also comes with a heavily modified take on Android called Color OS which may not be everyone's cup of tea.
Vivo X5 Max
Measuring in at 4.75mm, the Vivo X5 Max is the slimmest smartphone in the world. It is quite an interesting specimen as it does not skim on a lot of features and manages to provide a decent blend between high-performance and, well, the size zero factor. It has a speedy Qualcomm Snapdragon 615 CPU, 2GB RAM, 16GB of internal storage and also a massive 5.5-inch 1080p display, which in our opinion is quite vibrant. It has a 2,300mAh battery to boot, which isn't too bad considering its size. On the back, it also has a 13-megapixel snapper and a 5-megapixel shooter on the front.
Huawei P6
The P6 is yet to make its way to India, but it is one of the slimmest phones in the world at 6.18mm and is actually one of the nicest looking phones we have come across in a long time. It has a 4.7-inch 720p screen, a Huawei made Hi-Silicon quad-core processor, 2GB RAM and 8/16 GB memory option. On the back, the phone has a 8-megapixel snapper and on the front there's a 5-megapixel camera. It also integrates Dolby's audio technology. The phone runs on Android 4.2 Jelly Bean in tandem with Huawei's emotion UI.