Well, I actually have a D1 and just got the D4 today. What is it you want to know? The speaker on the D4 is way better, sounds good enough to actually play some music as background through the external speaker. Regarding phone calls, well all I can say is, when I got the first phone call on the D4 my immediate reaction was: WOW! Very clear voice, much better than the D1. So far I am VERY happy with my purchase, though - boy - this thing is loaded with bloatware! Cannot say much about battery life (my biggest worry since you can't swap the battery) because I have been playing with it non-stop for hours and with that kind of usage it won't make it through a full day. But that is to be expected.