Frequently iPhone Sync to iTunes on a PC or Mac does not transfer a Voice Message or other specific file. There are dozens of3rd party programs that are supposed to transfer and convert files, but some do not work and may corrupt the file - making recovery impossible. If you have trouble transferring a file the first thing you should do is a manual backup of your phone using iTunes (you don't need to change the default backup method, just do a onetime backup). Then protect that manual backup by copying the backup folder to another location, like documents. Manual backups in Windows 7 and Windows 8 machines are located in the folder C:\Users\[your username]\AppData\Roaming\Apple Computer\MobileSync\Backup\[random 40 alphanumeric folder name].
If you want to find a specific file in an unencrypted backup, like a Voice Memo file, you can do the following,
Open the 40 character named folder that has the most recent current "created on" date. You will then see hundreds of files with 40 character alphanumeric names and no file extension (like .mp4). Don't panic. There are now three possible ways to located the VM, you may need to do a bit of scavenger hunting to find the right one. Some people suggest copying the largest files to a new folder, renaming them with a .mp4 extension, and then trying to open them with Windows Media Player. If it is the VM you want it will start playing, if not you may get a file type error.
I have successfully used a slightly modified method. Sort the files on "date created" and/or "date modified". Identify files from the date you recorded the VM that are large enough to be media files (for a 10 minute VM the file would be 5,000 KB or more). There will be dozens of files that are not VM's, but one of the files is the VM you are looking for! Right click on the first file you think may be the right one, select "open with", and choose the free RealPlayer (my favorite), QuickTime, or Windows Media Player (warns about trustworthy sources - say ok). If it is the right file it will start playing, if not you will get some kind of error message. Keep testing files until you find the VM, copy that file to another folder, rename it to something simple with a .mp4 extension (eg - party.mp4) - and you then have a very high quality version of the VM. This is a lot of work but it prevents loss of important VM's.
Even if you use another method to find lost files ALWAYS do a manual backup first just in case the original file gets damaged