I use a big phone, the Samsung Galaxy Note 2 (and I'm waiting to order a bigger phone, the Nexus 6). I am capable of one-hand operation with it, but sometimes use two hands when it's convenient. Personally I don't have an issue with using two hands most of the time. Browsing, productivity, and game-play are best done in landscape anyway, which requires two hands on most any device. Phone and SMS/MMS are easily handled with one hand.