One thing i always like to ask myself is "why would I call this person back?" if you were on the receiving side of the call. Sometimes it's good to not over think it. Your company exists for a reason and has a product that was created for a specific purpose. Internalize that and try to communicate it in a few short sentences when you open the call or leave a voicemail. Think about why you would call your company back .
Living easy. Living free.