I don't like using iTunes it's bloatware on my PC and I like to use my iPad as if it is an Android device where I can access the file system and then move the files myself to where I need it to go, for example move them to my Google Drive account.
I've had a look around inside the file system but I'm having trouble locating where Zoiper actually stores the call recordings.
For comparison are use the Total Recall app on my Android phone and want something of similar functionality on my iPad. Maybe one day you will have the sync to Google Drive like it does.