The included tone control is a huge feature that really helps for many calls. It has plenty of amplification and 12 compatibility settings to allow it to work on many different phone systems - they claim 99% of systems. I've used it on Comcast phones and on a large business system and needed to change the compatibility settings. I'm guessing that any other amp without the capability to change settings (which may be all other phone amps) would have worked only on one of these two systems and not the other. I've used it on a 9 volt battery for 4 months, and it's still going strong. It also comes with a 9 volt adapter to avoid using batteries altogether. Beach Audio also rocks. [...]
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