Read Michael Usiagwu explain how you can protect your enterprise cloud phone system against cyber attacks on Infosec Magazine :
IP telephony has been popular among companies looking to transform their voice communications or make their existing communications systems more unified, but also need to ensure that they are secure. Since using a PBX or VoIP involves transmitting information over the internet, more safety precautions are necessary. Cloud telephony systems may be attacked through such means as phishing, call interceptions, impersonation and spoofing. You can only enjoy all the benefits of IP telephony if you have a strong defense system in place, and for an enterprise to have maximum security against cyber attacks, they have to maintain certain precautions.
Read his full article here.