If you buy the custom iPhone 4 dock, then no it won't fit with any case on it. but if you buy Apple's Universal Dock, then yes it will fit.
Apple's iPhone 4 dock retails for $29, but their is a thread that was started over the weekend (
https://forums.macrumors.com/threads/1042807/) with a great find. Currently RadioShack has on clearance the Universal Dock for only $19.97 (retail $49), and this will not only fit any current or future iPhones, but all of your iPods as well (a better buy), though availability varies per location.
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