The back pockets of your Classic pants can be opened if you wish.
Before choosing to open them, pay attention to the depth of the back pockets, by looking inside the pants. For aesthetic reasons, the back pockets aren't deep. Therefore, it is a good idea first to investigate whether the thing you intent to keep in your back pocket can fit.
Please note you can no longer return the pants when the back pockets have been are opened.
Here's how to open the back pockets:
1. Get your pants as well as a sharp knife or scissor
2. Carefully insert the knife into the the pocket from the side
3. Carefully cut across and make sure it is only the stitches you are cutting up
4. The pocket is now opened
5. Remove any excess thread that previously held the pocket together
6. You are now done! Do the same for pocket #2 and give yourself a pat on the back.
Should you still be a bit unsure, see the following guide: