Seems to be fully featured, but have had issues with the system (3cx) that I am using it with. The firmware on the phone I received was a bit out of date, and needed updating to work properly. Updating the firmware was quite difficult, but I managed it using TFTP and importantly i had to do an incremental update (first to 7.5.2b and then to 7.6.0), as a single update to 7.6.0 resulted in '...error 3: Buffer Full'.
For these reasons I wouldn't recommend this. We also had an older SPA508G which had the same problems, so unless you are familiar with Cisco products I would advise a different manufacturer (I found Yealink worked very well).
