Is there a way to keep my landline phones, modem and routers and get them interfaced?
I really don't like cellphones for voice calls. Besides I figure the stuff I have should be configurable.

There is an Ethernet adapter you can buy since the newer equipment uses proprietary connectors. I added a router to mine add more functionality. I’m unsure about your landline but everything else should work fine with it.

Is your landline VOIP? If so, use the above advice. If you need one, look into OOMA or others - you can move your landline # over. Make sure whatever service you use allows you to properly register your address for 911.

Thanks!