Earlier this year, after almost a decade of exclusively using mobile phones, I hooked up a landline and got myself a batphone. It's been fantastic.
With Google Voice, there's no more of that "call me on my landline, I'm at home" or "hey I'm running out, let me call you back on the mobile phone". I can easily make that decision by answering incoming calls on the phone I want to talk on, because Google Voice rings all my phones at the same time. Oh, and with Google Voice, you can get away with having only local (and not long distance) service, because even your outgoing calls originate with an incoming call.
Not only that, having a landline actually makes Google Voice work better. GV users are all familiar with the slight voice delay added when going through Google's pipes, so you often get awkward conversations where people talk on top of one another because the natural talk-silence-talk rhythm is thrown off. When delays are measured with milliseconds, having a landline helps reduce that latency issue drastically.
So having a landline is great for call quality and such, but that's only half the benefit. The other half? Being able to use a desk phone.
I'm not talking about a fancy wireless DECT phone, I mean a solid, old time phone. The kind they sell on rotarydialphones.com and redhotphones and other sites that dedicate themselves to salvaging older gear. The kind of phone that existed in the '50s and '60s and were reconditioned. Old Western Electrics - things that were solid and weighty and gave you gravitas when you had a conversation.
This isn't just about looks, this is also the way that these phones were made. They were heavy, but not too heavy to be uncomfortable. They fit your face. You could hold the phone by its grip or by the bottom if you were having a more serious conversation, or pressed up against your shoulder if you were making dinner. I don't know what it was about the design, but a corded handset feels marvellously better pressed up against your face than a mobile phone.
I love mobile phones - no question. And hell, you can even recreate the traditional handset experience easily. I'm just saying that there's quite a lot of benefits in sticking with technology that's been around for about a century. When the president gets woken up to answer the 3am phone call, he doesn't answer it with his mobile phone, he answers it at his desk.