New AT&T wireless phone

What do you mean it doesn't work? No dialtone, high pitched squeel ? If you have DSL then you do need to put a filter somewhere on the line to filter out the "internet noise". Do you have an old style POTS line with a phone number?

My new phones say "no line" on the phone screen, I've called my landline number from my cell phone and my landline phones don't ring. There is no dial tone, no connection. 

I've never cancelled my landline since I had it activated a year and a half ago ps

If this is a traditional landline test it from the NID.  If you're using digital service than the phone plugs into the phone port on the back of the modem.