Telephone Call Volume

I find it very tiring and stressful to engage in a telephone conversation in which it is difficult to hear the other party, for whatever reason (more often than not, because they are habitually speaking too softly). It would be a very, very nice feature if phones could dynamically adjust for loudness--amplifying quite voices, and muting loud ones. That would be some fairly sophisticated signal-processing, but in this day and age, it seems possible.