This is a work in progress, and certainly not the best possible way, but I think it should suffice.
So we're finally deciding to ditch the landline, and switching over to mobile phones. But because of budgetary contraints and since we generally don't use the cells enough to warrant a plan, I had to come up with a good method to keep everyone connected for as cheap as possible. This is what you'll need if you're interested.
1) A broadband connection with Wi-Fi
2) A Skype account
3) An Android phone
4) A google Voice account
Costwise, it'll be about $140 for the phone, $30+ for the Skype subscription (annual), and whatever you pay for your broadband. Naturally, if you don't already have broadband, or a computer, it's not very cost effective at all. But for my particular case (broadband and computer a necessity), the mobile solution got a lot easier.
So, to start things off, what I did was to purchase a prepaid phone with Android. You can actually get a refurbrished phone from T-mobile for 99 bucks, but I ended getting my wife and mom new T-mobile Comets for about 120 bucks. Because the phones work on Wi-Fi, I turned off the 3G and all my data goes to my phone via my home Wi-fi. I downloaded the Google voice and the Skype app.
I already had a Skype account with Unlimited Nationwide calling for about 30 bucks a year, it's basically a subscription that allows you to call anyone using Skype (computer or in this case, Android phone) to anyone in the US, landline or mobile. It's not a bad deal with the computer, an even better one with the Android.
Then, I got a google voice account with a local number. What Google voice does is a little hard to explain, but basically it's like smart voicemail. Say my number is 555-5555. If someone calls that number, GV will forward the call to any number of mobile phones, like me and my wife. If either of us answers it, it stops ringing. If nobody answers it, it goes to voicemail in GV and it can email you the message or you can access it on the computer. It also has a transciption thingy but it's rather buggy. So what that means is that to check your voicemail, you don't have to use your cell minutes, just use your broadband to check the messages.
So with all this setup, when I make a call at home or anywhere with Wi-Fi, I call the number, choose skype out, and I'm talking via Wi-Fi. No minutes used. When someone leaves a voicemail, I reject the call, it goes to google voice.
There are limitations because I can only use Skype to make calls via Wi-Fi. When I receive calls, it will cost me minutes so basically I have to be the one who calls. Also, Skype's a little buggy on the Android. It stays signed in, and then for some reason it gets stagnant and doesn't want to place calls a few times. You basically have to kill Skype before you make a call, which is a free app at the Android store.
This hasn't been fully implemented, but I'll be sure to update if it does/doesn't work out.