Can I use my iPhone(s) to answer landline calls?

Hi,

My landline handsets are coming towards the end of thier functional lives..... and I need to replace them. The thing is that we rarely use the landline, but have three handsets/chargers as our house has three floors. Ideally I'd like to get shot of all of them and replace them with a device that can route landline calls to our Iphones, without making use of call forwarding/divert which will chew money up on my landline account.

There are quite a few devices that allow mobile calls to be recived on home phone handsets via bluetooth, but I'm wondering whether there is something that will go the other way.

Thanks.