Hi,
I was the one who returned my D3 due to severe RF interference in my region.
I live in Singapore, and it is a densely populated country. We're not as bad as Japan or Hong Kong, but close enough.
I believe it also boils down to the GSM or 3G modes of mobile service our carriers have chosen to adopt.
My Sony Ericsson M600i does in fact interfere but not as frequent as my iPhone. Though I do not use the phone as my primary source, the fact that you have them in the same bag, the phone and the amp with DAP, does not take away the RF problem.
And everyone else's phone in the train or public will have the same chance even if you leave home without one.
To me, the idea of having a portable amp is to carry it around to enjoy. If RF is going to restrict my Amp to only for home use, I don't see how that works out even if the sound is amazing.
I have to place my phone near me and in Vibration mode. I tend to miss calls or text messages while listening.
Regards.