I Just got a hold of a brand new Samsung Gear VR headset. Wanting to try it so very badly, but I do not have a Note 4. I figured I would try my nexus 6 first since this has a better display, but this phone is slightly too big to fit. Next up was my retired Nexus 5. It fit in nicely. I have a cheapo s-curve case on it, so it helps fit it better(2$ from ebay) I also used some cloth in the back to keep it from moving around.
I ran a few 3d demos with it and it worked great. I can see the full view of the lens and the 3D effect is perfect.
The Gear VR opened up with the Nexus 5 in front.
Padding I used to hold the nexus 5 in place.
Issues: The Gear VR is only being used for their lens (the usb and built in sensors+touch interface are unused). Basically a very expensive version of Google Cardboard, but these are way better feeling. Also you can adjust the focus of the lens. Last issue is that you can't press on the screen once the phone is in so you have to use a controller to navigate any menus and launch the game before you insert it.
I tried fit checking some other phones I had. The S3 and S4 seem to fit. The OnePlusOne fits with no case. I didn't try the 3d on them.
Now next step is some Thermal 3D action with the flir lepton.