via Teaching without Walls. Here is an article about a tool called SpeakPipe, which allows students to leave voice mail messages from your web site:
http://www.teachingwithoutwalls.com/2013/12/speakpipe-online-mobile-voicemail.html
I am currently using Livehelpnow for online office hours and help sessions, but SpeakPipe might be something to check out for next semester. What contact tools or online help tools do you use?