Well I found out how to get acceptable to very good stereo on the iPhone. First I explain what I use:
- Fostex AR 101 that comes with 2 directional mini stereo microphone
- 2 rode Lavalier omnidirectional
- cables: 2 x 3.5mm male - female TRS cables, two "y" 3.5mm male and 2 female TRS 3.5mm jacks adapter.
Connect the cables male jack into the two microphone jacks of the Fostex AR 101. On the other end of the cable connect the "y" adapter. The "y" adapter has two female 3.5mm jacks, 1 is for the Rode Lavalier and the other you connect the mini directional microphone. So two directional on the chest and the two rode Lavaliers attached to the male cable jack make that you get great stereo sound. You get the sound of the whole area and every word you say will be displayed very clearly.
The Fostex cost prices = +- 150. Euro, the adapters +- 30 euros and the rode Lavalier 170 euro each without Micon 2, 3.5mm adapter. It is claerly, the Lavalier is the high cost. There are cheaper Lavaliers that seem works great but myself do not know the level because I never use Lavaliers from other factory.
I'm not musician, I wanted only stereo using video apps on the iPhone. As I said I do not know the audio results with cheap Lavaliers or battery powered mics. Rode is indeed an expensive Lavalier but it can be cheaper with the Smartlav were is also needed the KVConnection, SC4 or SC3 adapter, just check it out cause I'm right now not able to do so.
It is possible to get low budget stereo in comparing DSLR camera and expensive Rode stereo VideoMic of how call it.