Intermittent Dial Tone on Land Line

Several friends have tried to call me, saying they either get a busy signal or the call never goes through. I have noticed throughout the day I have no dial tone. Sometimes I do, sometimes I don't. I've disconnected the line several times and that works to restore dial tone occasionally. Other times I've started a trouble ticket with AT&T and half way through the process the dial tone returns. I'm getting tired of constantly checking my landline for dial tone. All connections seem to be in working order. Any suggestions?