Recently, I upgraded my home studio with a Behringer mixing board and Sennheiser microphones. I did this for two reasons. First, I wanted to start producing some professional quality podcasts. The mixing board and microphones make professionally produced audio possible. Secondly, I wanted to be able to go to remote locations and do live broadcasts (video and audio). That is why I upgraded to the USB soundboard so I could run the audio through my computer and directly into my broadcasting/recording software.
I didn't, however, think about how this would create better audio on my phone. The best part is it is so easy to do. As with anything, the higher quality equipment and the better your audio will sound so don't skimp on the microphones. These are Sennheiser e835's and they are wonderful. With a few adaptors, cables and microphones you will be ready to go!
Connect your microphone to and XLR cable, connect cable into one of the Y adapters (repeat for the other microphone if needed) and connect the Y-adapter to the iPhone/XLR adapter. Plug the iPhone/Xlr adapter into your phone and that is it!