I have the following phone amplifier:
unfortunately, it has problems.
If I bump the volume up too high it gives feedback. If that wasn't bad enough, the feedback is audible to everyone else on the phone too. I'd like a device that amplifies the volume while also filtering out feedback if it occurs.
The top volume is usually too loud, but when I'm on a phone conference, some of the speakers speak softly and some loudly. I'd love if the phone had a volume normalizer so that all sounds were within a certain volume range.
A mute button (for my headset) would be handy, but it's not required.
There's also a lot of white noise if the volume is boosted too high. There's probably no way to prevent that, but if the device had some sort of intelligence that filtered out some of the white noise then that'd be nice.