From "tel: 07773403290" [firstname.lastname@example.org]I was not able to determine if there was any body text from my sample collector, however each sample had an identical attachment message_01983527496.wav.zip which contains a malicious executable message_01983527496.exe. This has a VirusTotal detection rate of 5/55 and automated analysis tools   show it POSTing to:
Date Thu, 06 Aug 2015 11:54:43 +0300
Subject RE: Voice message from 07773403290
This is hosted on a RU-Center IP address of 188.8.131.52 in Russia. Furthmore, a malicious executable is downloaded from the following locations:
In turn, this has a detection rate of 2/55 and automated analysis of this   show that it phones home to 184.108.40.206 (Web Hosting Solutions, Estonia).
The payload is unclear at this point, but you can guarantee that it will be nothing good.