I have Virgin Mobile and the 3g signal doesn't seem to be good enough, I was able to fix volume issues by adjusting the microphone and speaker, also used echo cancellation, but there persists a delay even with "keep active," and sometimes things break up when the signal must be weak.
I'm thinking of getting the HTC Evo which allows 4g on the Sprint network (Wimax). Based on the coverage map it looks like I should get 4g in my area. Do you think this would solve the delay problem? Has anyone else been in this situation and did upgrading help?