Despite an impressive lineup of high-end devices like the Lumia 1020, 1520 and Icon, all of Nokia's—indeed, Windows Phone's—market share gains in 2013 can be attributed solely to low-cost, low-end devices, primarily the Lumia 520 and its derivatives. And since it's fair to think that this situation will continue in 2014, Nokia is facing this new year with a more diversified lineup of devices that target that part of the market. Key among them are the Lumia 630 and 635.
As their model names suggest, the two are quite related, and they do indeed share the same bodies and major internal components. If you're familiar with Nokia's previous Lumias, you may wonder how these phones relate to the Lumia 620 (the original low-end Lumia and a predecessor, by about a year, to the 520) or the Lumia 625, which is a low-end device with a big (4.7-inch) albeit low-res screen. They're clearly successors of a sort to those devices as well, and given their screen sizes, the 625 is perhaps the more obvious comparison.
Lumia 630
Where they differ from each other is in the radio: The Lumia 635 uses the sort of LTE radio that is standard in Western Europe, the United States and other mature markets. But the Lumia 630 is the first Windows Phone handset to utilize dual SIM card slots, a key feature for emerging markets where customers don't sign lengthy wireless carrier contracts and instead jump from carrier to carrier regularly.
Lumia 635
On that note, we'll get the Lumia 635 in the US (on T-Mobile and Metro PCS, at first) but not the 630. And looking beyond the differences, you'll see the following identical features between the two:
Processor: Quad-core 1.2 GHz Snapdragon 400.
RAM: 512 MB.
Storage: 8 GB.
Micro-SD expansion: Yes, up to 128GB.
Display: 4.5-inch FWVGA (854 x 480) ISP screen, which is a new resolution for the previously restrictive Windows Phone.
Main camera. 5 megapixel with 720p (HD, 1280 x 720) video capture at 30 fps.
Colors. The Lumia 630 comes in white, black, green and yellow, while the 635 comes in all of those colors plus orange. Each can be replaced with a different color case.
So like the Lumia 625, these phones feature a large but low-res screen, which is what puts them in the entry-level part of the market.
