It is being replaced by VoIP service and wireless. In my opinion, as the infrastructure supporting both networks matures there will be an even faster migration away from wireline providers.
Besides the dramatic cost advantage over wireline services, customers are taking advantage of more features and better access to their accounts. They can manage their bills and make changes to their account online.
The trade off right now is quality of service. Analog lines still offer an advantage when it comes to reliability and better audio. However, this will change over time. Remember, the data networks were never designed with voice transmissions in mind.
The network engineers are playing catch up when it comes to voice, but the demand for better and more reliable service is driving the need for more improved voice networks.
The best is yet to come.