This feature is available with most, if not all of the other PBX's and phone services for Free. Why would you not provide this with the Free Version and require potential and exisiting customers to pay for this feature. This seems to be a rudimentary function and goes hand in hand with Voicemail support. I have the free version installed and to date have been pleased, but still compare to trixbox on a regular basis. This feature is provided by Trixbox for Free.