It's pretty clear after a few minutes of handling Speck's new ToughShell for iPhone 4 ($50) that this new case -- released more than a year after the only iPhone that sits inside -- was one of those challenging, "keep on tweaking 'til we get it right" designs. As a rival to OtterBox's Defender, Griffin's Survivor, and other multi-layer reinforced cases, ToughShell is a considerably more advanced design than Speck's earlier ToughSkin, which effectively…
