LG VX-8700

I recently purchased the 8700 and am enjoying it. I read in previous posts that this phone does not support side-tone (hearing yourself when you are talking to someone else). During some calls, I have side-tone/can hear myself, however, on the majority of other calls I can not hear myself at all. Does anyone else experience this or have an explanation for this? I am coming from an 8300, which had the side-tone and thought it was a positive feature for a phone. Thanks for any input or help.