Google controls my life and my GTD system. I use the gMail app on my iPhone, and yes, I process to zero every time I look at my mail on my phone.
I employ a variation of what Kelly suggests above, on the principle that sometimes "2-minute actions" will be shorter than two minutes. In this instance, it's not necessarily because of time, but perhaps because I don't want to send important correspondence from my phone/don't have the attachment, etc. If I process email from my phone, anything I can't or don't feel comfortable answering from my phone I simply tag "@action" to deal with later.
My phone has become a crucial piece of my inbox zero process. I also use Priority Inbox, and will often process my "Unimportant but Unread" emails while travelling. 90% of those are, "Might be interested, want it to come across my radar" kinds of items (LivingSocial deals, coupons for the craft store, etc.) and they can be dispatched with quickly. The phone is aces for that kind of processing.
Collect. Process. Organize. Review. Do. That really is all there is to it.