I'm a newbie to Raspberry pi and I'm currently working on project and what I need is ,real time transfer analog call to mobile application over WiFi. So can someone suggest a way to accomplish my task? Do I need additional hardware or using a simple code can I make this work? Thank you.
You need a so-called FXS adaptor. You also need PBX software to go with it. Cheap USB FXS adaptors can be had online for 50-60 $. There are several dedicated Raspberry Pi PBX distributions available , the most popular being the aptly named RaspPBX which is based on the open-source Asterisk system.