Freecall only supports Windows as the base system, so if wine isn't working, then your only option on Linux is running Windows inside of VMware or VirtualBox. Even so, audio access from within a virtual system can be a problem on certain PC's.
If VOIP is the only reason for switching to Linux, then you should actually switch back to Windows. Freecall is by no means free software (do not confuse their free client software with Stallman's definition of free software) or open source - it simply belongs to the dark side. If you are refusing both Ekiga and Skype, then there are no other options, I guess.
Maybe launch your own project: write the software, buy and maintain all the servers, make it work on Linux, and make it free for everyone. Sounds good!
Arch Linux