I have Mediacom Internet service. It is a TV and Internet Cable service provider. I collect and use antique phones and retro phones from the 60's and 70's that have the old fashion bell ringers. Phone service through Mediacom is VOIP phone service that runs over the Internet. The cable modem that also has the phone connection to connect to the house phones and provide the phone signal to your phones is not very strong. It can run all the new modern electronic phones without issue, but might be able to just power one old fashion bell ringer phone, or after adding 2 phones with real ringers it stops working and can't ring the phones. This device resolved my issue, I have four phones from the 60's and early 70's with real bell ringers and they now all ring and work. Also for anyone with such a phone service with rotary phones, you need to also add a pulse to tone converter to the rotary phones. So if you switched from regular POTS line telephone service (you have phone wires that connect directly to the phone company like AT&T) to a service that provides phone service over the Internet and your old fashion phones with actual bell ringers in them stops working or can't be used on your current phone service, this will fix your issue. I am please to have bought this item. It allows me to be able to again use my antique / retro phones.I have an EZLinq VOIP adaptor from NetTalk that by itself won't ring my 4 desk phones and a couple of wall sets, all with real ringers. Assuming each phone with a ringer draws one REN, I'm 2 over the advertised 4REN and the phones are ringing like the Bells of Hell! Good job Viking!