Am also using 3G and almost always CW. Settings I use are audio quality 0 - alaw 8 Khz, Rx jitter buffer 15, jitter delay 14, audio packet size 10 and on keyer settings lf delay 650 and key delay 200. With these settings I can cope up to 200ms latency - if it goes higher than that I start getting dropouts. These may not be optimum settings, but they are the ones that work best for me.
73 Dave EI6AL