With the sound button already on full, how can I increase the volume of callers voice? I can hear the voice OK for some people. But others are borderline and too often I have to ask people to repeat. I don't think the problem is with my phone so much as that my ears are getting less sensitive. But a louder phone would help. Under [settings] [volumes] I have four controls set to the maximum, but voice is not listed. Droid RAZR MAXX HD.