My home office needs a landline - it's the only way to answer the door in the property, as the intercom at the building entrance dialls the occupants for authorisation. I've been looking for a way round this, as I object to paying a not insignificant monthly fee simply to answer the door. We really have no other need for a landline. It's possible to link a mobile phone number to the intercom, but then only one of us can answer the door!
Voice-over-IP has provided the solution. We now have a free SipGate Basic account which operates on a pay-as-you-go model. To be able to continue using our existing handsets I bought a Cisco SPA112 box. This creates a bridge between VoIP and traditional handsets. I didn't want to get rid of the handsets for the same reason I couldn't simply link a mobile phone number to the intercom - it restricts who can answer the door. We often have a need for guests in the house to be able to answer the door.
There are a couple of additional benefits as a bonus:
It's all working very well, more convenient than before and no more landline tax.