I have two setups for this phone. When I use the standard battery, I use the Seidio Surface case combo. With the extended battery, I use the Otterbox Defender, modified. Don't worry, as there is no permanent physical modification of the case. I just don't use the hard portion of the Otterbox on the rear of the phone. The hard plastic piece goes on the front and the silicone piece goes on the back. Fits nice and snug and works with the clip. Use this setup all the time. If you search this forum, there is a thread with pictures...Highly recommend and would use the Otterbox exclusively if it wasn't so big this way.
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Sorry, I did mod the Otterbox slightly. I use a Zagg Screen Protector, so I did remove the built in screen protector on the Otter.