Measure the call sound quality using Discrete Fourier Transform

Question

I need to measure the sound quality of calls made between two mobile devices. I found out two ways to implement it.

1. Test it with a sine-wave at 100hz frequency increments between 300hz and 3.4khz. If there is a clean Signal-To-Noise ratio for all/most frequencies, it can be assumed that the call quality will be good.
2. check the bottom of the spectrum (300hz), the top (3.4khz), and a few random middle frequencies to see if those transmit with a clean Signal-To-Noise ratio. If so, it can be assumed that the call quality will be good.

I don't know how to get this sine-wave? Should I use DFT? If yes, I have three below questions:

1. Does DFT uses the signal of mobile network is being sent by tower to transform it into waves?
2. If yes, how to find the signal and give it to DFT function to work?
3. If no, should I give the sound signal to DFT function? How to find the sound signals? Do I have to make a call and record them?

If the solutions I made are not correct, please help me figure out a good solution.

Thanks in advance.