I loved the design by @muzz64. I used the same principle to make a customized version to fit the Iphone 4 cable.
I wasn't sure how to model supports like the ones muzz64 used, so I relied on the software generated supports instead.
EDIT: I've added a less steep version which is easier to print, for those having problems with the overhangs in the original.
Use 3 perimeter layers for strength.
I printed mine at 0.2mm layer resolution for the lower bit, and 0.1mm for the coil above. It doesn't really matter though. Use whatever makes sense to you.
I wasn't really sure how to design a support the way muzz64 has done on his original model, so you'll have to rely on software generated support. Just don't make them too dense in case they become difficult to remove.