Nokia 3100 / 3120

Volume control on the 3120 is the right > key to increase and left < to decrease. It must be done during a call in progress for some unknown Nokia logic. A graph will appear when you're setting it to show level.

The good news is it will stay where you set it for future calls. This info I found buried in the Manual that came with my phone. It is worth reading to discover other 'dirty little secrets' Nokia choose not to make intuitive in the software.