We researched this recently and there are a few different techniques. The cases with printing on the sides are usually sublimation that is vacuum heat pressed onto preformed cases. If the design is just printed on the back, it could be sublimated on a aluminum/plastic insert and then glued to the case.
You will need at least $10k for equipment and supplies for the vacuum press and printer and it will only press about 1 every 2 minutes not including printing time. If you want a production oven setup, expect to shell out $30k for a turnkey system.
If your happy with just printing on the back, Conde Systems has some packages that use a sublimation printer and heat press .
In the end we ended up going with Case-mate. They have a B2B program and use the vacuum press system for printing on all sides. You upload design, they print and ship to you or customer. Less profit per piece, but much less work and no overhead.