This is probably the biggest drawback to installing a camera lens that requires an external case. If you do not currently have a smartphone case installed on your current phone, it is not a big deal at all. But, you may be quite fond of your current case and not willing to remove it. However, just as the designers of the olloclip lenses point out, it is pretty much impossible to design a lens that is compatible with every smartphone case in the world. You simply can’t expect this to be done and as such, you may be forced to go with the manufacturer’s specific case.
To be honest, though, most of these cases will more than suffice. Or, if you opt to buy the lenses separately, you could take a risk and see if your smartphone case will be compatible but that could be a long shot.