At a glance I couldn't figure it out; I read the manuals but I still couldn't understand how to open the HTC3600.
Here is where I think the problem is:
- the HTC3600 quick guide only make a reference about "sliding" the cover, but doesn't tell you in which direction
- "sliding" the cover doesn't seem like an option because it looks like the camera in the back won't allow such motion
- the cover could be really tight on some units (at least until you open it a couple of times and it gets loose) and you're afraid of using the force and risk breaking a 600$ phone
Sounds a bit stupid, doesn't it? Well, I've search the net and so I've discovered I'm not a complete idiot, as many other people had the same issue...
Eventually, one post pointed me in the right direction. Now that I know how, it's easy to open it (it even opened by itself when I dropped it on the carpet :-))
Anyway, since many people looking for a solution asked for pictures, I decided to post this blog note.
The manual is right, the cover does slide in the direction indicated by the arrow.

However, it will only move for 3-4 mm in this direction, and then it will stop.

After that, the cover can be lifted and set aside. Notice the disk around the camera lens is just a cover (not the real lens), and slide together with the HPC3600 cover.

To open the phone you may need to use a bit of force. Here is how I think you can open the phone easier:
- remove the stylus from the phone (the stylus doesn't slide, and it will make it harder for you to grab just the cover and slide it)
- take the phone in your left hand as indicated in the picture below (with Call/Cancel buttons towards the palm, and left wrist)
- use the right hand index and thumb fingers on the upper/bottom and apply presure towards the right side while holding the phone in left palm
- the cover should slide 3mm with a click, then stop
- you can now lift the cover