Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
If the phones are turning On, and seem to be responding OK, but you get no phone signal or cannot dial out on your line - *and*, if you have DSL/ADSL service and a DSL modem - then you do need a DSL filter.
They are usually provided in your DSL modem's install kit. Look for a small 'dongle' with a short phone cord at one end. Probably several were provided in your DSL modem's install kit.
If there are none, contact your DSL/ADSL provider. They should have provided you with enough of them, perhaps they will even provide another free of charge... but they are the first ones to contact about getting a DSL Filter.
Let me know how it goes, and what you think... I will offer further advice as needed. Thanks.