The latest WP8 supports bluetooth communication to serial bluetooth modules through serial port profile(SPP). This mobile app works only on wp8 devices such us Lumia 52, 620, 720, 820 and so on. For full list of wp8 devices check this link. The mobile app code is written in vb.net.
The AUBTM-20 bluetooth module is used in this project. It works only on 3.3v, so i am using the AT89C2051 microcontroller which can work on this voltage range.
You can download the App from windowsphone app from this link.