I'm intreagued by this use of mobiles from the cockpit. In the Chippy or the Yak youd have no chance of hearing it unless it was somehow wired into the headset.
While I can't hear the mobile phone in the Jodel cockpit, people who have called me say they could clearly hear my reply saying when I'd be on the ground. With an earphone in position it'd be possible to use it.
I bought my Icom with a headset adaptor and have never had a problem with it. Without a headset it is useless with the engine running.