Just got mine and it is a 3520A ... I think that the 3520 is the same, identical. I am sure about that. Perhaps the only difference could be the firmware, which you could flash to a newer version once it comes out. In my opinion, there ain't no difference. However there is a big difference between the NEC 3500 and the 3520 (3520A ). Nec 3500 being the older sibling with some issues (nothing serious though).