Phone Calls Encryption for Businesses is the topic.

Topic Description
One of the ways to secure the phone calls through encryption is through the use of VoIP technology. This technology consists of two or more (for conference calls) IP phones and IP network that can be connected to traditional phone system. The technologies goal is to not allow person or people to intercept (tap) the phone call at its various points.
The Reason for the chosen topic
In a last couple of years there was rise in interest towards safety of data transmitted through phone calls, especially in respect with latest information regarding NSA collecting data about peoples phone calls. So we chose this topic because we thought it would be interesting to see if phone call encryption technology really works and if it provides significant benefits to the businesses who use it.
Paper Outline
Phone Call Encryption
How Phone Call Encryption Works
Benefits of Phone Call Encryption for businesses
Problems with Phone Calls quality caused by Encryption
Cost of Phone Call Encryption
Worthiness of Phone Call Encryption based on security of data vs Cost.

here are some references you can use it with other references that you spouse to find:
http://www.theverge.com/2014/7/29/5945547/signal-brings-painless-encrypted-calling-whisper-systems-moxie-marlinspike
http://www.washingtonpost.com/blogs/wonkblog/wp/2013/06/14/nsa-proof-encryption-exists-why-doesnt-anyone-use-it/
http://www.cellcrypt.com/deployment
Mobile phone calls as a business risk. Network Security Journal, Volume 2010, Issue 9, September 2010.

The Journal of Supercomputing.
http://www.technologyreview.com/featuredstory/526496/ultraprivate-smartphones/

talk about this topic as paper project.