How are the two smartphones different? Here's the nitty-gritty: the Lumia 630 is available in 3G single-SIM and 3G dual-SIM variants, which is finally made possible in Windows Phone 8.1. Meanwhile, the Lumia 635 is a single-SIM only, 4G/LTE-connected smartphone.
Microsoft recognizes the importance of dual-SIM functionality for their customers in the developing markets and has given special attention to it. The dual-SIM Lumia 630's home screen is graced by two individual tiles for each SIM card. Each card can be separately assigned to work only with specific contacts, so users can, for example, call their family and friends through one card, and call their business contacts through the other. This way, different contacts categories can be kept in two separate communication zones, so to speak.
Overall, the Lumia 630 and 635 do seem like uncompromised entry-level devices. While we would have been thrilled to see Microsoft bump the RAM to 1GB, Windows Phone 8.1 should be able to make do with the available 512MB. The 5MP rear camera is ho-hum as well, but that's pretty good for an entry device.
Stephen Elop announced the pricing and tentative launch times as follows: the Lumia 630 and 635 will be launching between May and July 2014 in worldwide markets, priced at $159 for the Single-SIM Lumia 630, $169 for the dual-SIM variant, and $189 for the 4G-enabled Lumia 635. T-Mobile confirmed that it and MetroPCS will be offering the Lumia 635 in the USA this summer, while T-Mobile's Nokia Lumia 521 and Nokia Lumia 925 owners, as well as MetroPCS customers who own the Nokia Lumia 521, will be updated to Windows Phone 8.1 in the summer as well. AT&T also confirmed that it will carry the Lumia 635 in the summer.