I have not had any problems with the other person hearing me using my Lifeproof case for my phone. I also use a Bluetooth, the Plantronics Legend. But with or without the Bluetooth I have had no issues.
I had the lifeproof case on my 4s and now have it on my 5. I tried out the otter box but it was just to big with the case on. It is a really nice case. Otterbox now makes a waterproof case also for $99.00 on their website. Bit as I said I have the lifeproof case and love it.
I upgraded to the I5 in June , so I have had it 1 month now. I have had absolutely no issues. Plus upgrading at best buy I got a great deal and went from a 16 gig to a 32 gig for $30.00. They bought my 4s from me and applied that toward the new i5. In the end my total cost was a stunning $29.99...