Explanation of circuit and hardware components:

I used DTMF decoder module using MT8870DE and connected it to arduino as shown in circuit diagram. I pulled up(set on +5v) pin13 permanently so as to provide +5v to the module. As can be seen D1-D4 are connected to pin12-pin9 respectively, here D1 represents least significant bit and D4 represents most significant bit. Pin8 of arduino is connected to STD pin of DTMF module, it becomes high whenever a new signal(valid tone) is given to module.

Tones were generated via mobile phone and were fed as an input to DTMF decoder module using 3.5mm audio jack.

For motor driver I used L298D module here M11, M12 and M21, M22 are connection for LEFT and RIGHT motor respectively, when car is seen from back to front. Car will move forward when M11=M21=HIGH and M12=M22=LOW. With this information you can easily use my source code directly by changing your connection respectively.

PWM1 and PWM2 are the pins which can be used to control left and right motor's speed. I set both of them HIGH in order to attain maximum speed. EN1 and EN2 enables left and right motor when set high, so I shorted them with +5v supply from arduino.

I connected Vdd for DC motors to a +12v supply.

Phone was mounted on servo motor. Data pin of servo was connected to pin5 and +5v was taken from +5v supply and not from arduino as the current drawn by servo motor that I used exceeded the maximum current that could have been drawn from arduino.

Explanation and working of peripheral applications used:

First of all I connected my laptop and my mobile phone to the same network.

I used DTMF Tone Generator to generate DTMF tones. This application was running on my mobile phone.

Now in order share the display and gain control over my mobile phone from my laptop I created a VNC server by running VNC server application on my phone in background and using VNC client on my laptop, now I was able to view my mobile phone's screen and simulated touches from my laptop.

At this point I was able to generate DTMF tones from my mobile phone using my laptop, therefore I was able to control my car using my laptop.

To get the live feed from my phone's camera I used AirDroid application, which was running in background alongside VNC server and using any browser(preferably Chrome) on my laptop I was able to use the camera of my phone.

Explanation of source code:

Source code is well documented, all the required explanation is given as comments.
Source Code