Are you using DSL? It sounds like you dont have filters on all of your phones. Each phone that is plugged into a phone jack needs a DSL filter on it, as well as the DSL; It needs to be plugged into a filter as well. You should be able to get these from your phone company or broadband provider. When you are online and your phone rings, the phone signal will cause interference with the DSL signal and cause it to drop.
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Are you using DSL? It sounds like you dont have filters on all of your phones. Each phone that is plugged into a phone jack needs a DSL filter on it, as well as the DSL; It needs to be plugged into a filter as well. You should be able to get these from your phone company or broadband provider. When you are online and your phone rings, the phone signal will cause interference with the DSL signal and cause it to drop.