I searched the internet to try to solve your issue, and unfortunately I didn't really find much.
While searching, I came across a forum about voipstunt, and someone said that you could view your call history from your account ( which from what I can gather you have to have in order to use the service ).
Also looking on the https://www.voipstunt.com website, their help section isnt very helpful at all, but they did mention that they only keep call history for 6 months. If you have a problem getting your call history I would strongly suggest contacting them.
Also .. you should really look into using Skype, or if you and your spouse have access to WIFI, there are plenty of smartphone apps that allow you to talk for free via WIFI ( with call logs ). Example : Viber, Tango, MSN messenger, yahoo messenger ... just to name a few
