In my opinion, the VDV-21 is one of the best value ATA available, and it's even have an LCD display to show all kind of information.Make it work is not easy, you have to start on website voipfan.net/unlock.php
Follow the instructions, however at the end the provisioning with an xml file can be done differently.
Google for "baby-web-server" and it can be used on a Windows PC to upload the provisioning xml.file.
Attached is the working FPL provision XML file, rename filename to "brcm<device-mac-address>.xml and just change your FPL info >username/password< (use notepad/notepad++/textpad)
The settings are for North-American 10 digit local/long distance dial, and EST timezone.