I was actually thinking about using the NTG2 connected directly into the GH2 with an XLR to mini jack adapter cable. Doesn´t the GH2 have a sound monitor "graph"? I know it´s not a pro solution, but couldn´t it be used to monitor the audio from the NTG2?

This is what I ordered for the GH2, haven't tried it yet:

Sescom iPhone/iPod/iPad TRRS to XLR Mic & IPHONE-MIC-1RA B&H

Are you planing to use it on the iphone or directly on the GH2?
Please share your thoughts once you get it.

The rep at B&H said it should work with the GH2 'in theory', so we'll see how it works
in reality.

This is what I ordered for the GH2, haven't tried it yet:

Sescom iPhone/iPod/iPad TRRS to XLR Mic & IPHONE-MIC-1RA B&H (http://www.bhphotovideo.com/c/product/813384-REG/Sescom_IPHONE_MIC_1RA_iPhone_iPod_iPad_TRRS_to_XLR.html)

Good luck but I doubt it will work for you.... the pin connections for iphones / ipads are quite different than camera inputs.
The cable you have indicated uses a TRRS (4 connections) not a TRS connector (3 connections) normally used as a camera stereo input.

This shows the 4 connections used for some apple products.
Universal 4-pole Cell Phone headset pinout and wiring @ pinoutsguide.com (http://pinoutsguide.com/HeadsetsHeadphones/blackberry_9700_headset_pinout.shtml)