The Lumia 640 will offer HSDPA+, Wi-Fi, Bluetooth 4.0, dual SIM capabilities, support for digital TV (which seems to be quite popular in Brazil), and a 2500 mAh battery. We don't know if the handset will run Windows Phone 8.1, or Windows 10 at launch.
The name of the Lumia 640 suggests that the smartphone is the successor to he Nokia Lumia 630 and Lumia 635, both of which will soon be 1 year old. A Lumia 645 will probably also exist, and, like the Lumia 635, this model could feature LTE connectivity, being made for the US market.
Microsoft might want to announce the Lumia 640 and 645 at MWC 2015 next month. These could become the company's fourth and fifth own-branded smartphones, after the Lumia 535 (pictured above), Lumia 532, and Lumia 435. We'll keep an eye on this, and let you know more as soon as new details arrive.
source: Janela Tech (translated) via Windows Central