I'm just learning SolidWorks and thought designing a cell phone case would be a great first project.

So I've modeled my cell phone and all its buttons in xDesign as a part.  I've 3D printed it and validated it against the real phone as a reference to build the case around.

I mocked up just a simple case for a starter part in xDesign.  Now I would like to bring my phone guide shape and my case shape together in an assembly so I can see where the phone features are while I work on the case shape.

I've inserted the case into the phone workspace and they've come out mis-aligned.  Again these parts will be fit together but they're really never the same assembly: there isn't any logical joints or rollers or any kind of machine join between the two.  

I cannot for the life of me figure out how to get the x, y, and z origins of these two models to align.  How do I move one or the other in the Z and X directions so they align?  Somehow the x-z planes came out right but I can't tell you why. The phone is hovering well above the case part and mating the origins of the two models won't go.  I should be able to just grab one or the other and move it along an axis freehand.  But neither will budge.  I've tried anchoring and de-anchoring, locking and unlocking.  I'm quite literally stuck.

The phone's not really symmetrical in Z so if I had to create a midpoint plane through it that would not be ideal.  

And I don't want to align the front face of the phone to the top face of the case model because the case needs to be proud to the phone screen.  Nor do I want to align bottom planes because again: case needs to be proud in all directions.  And there's not really a flat surface all the way around the x-y directions between the two parts.  And I'm not expecting the mid x-y planes of either part to align either.  

I need to establish a common x-y plane and a common z-y plane and move both parts to different yet fixed offsets from them.  Ideally the origins should coincide but I can't seem to budge the origins.  Somehow the parts are aligned on the x-z plane perfectly but I can't tell you why.

Please advise.  I'd be relieved if I could just somehow manage to move one or the other part AT ALL in this assembly.