I'm pretty sure the only way you would be able to do that is if you used Skype to make and recieve all your calls. You would have to get a Skype number, then pay the $2.99 for unlimited U.S. calling. More conveniently you could port your cell number to Google Voice and then have that number ring your Skype number. Whenever you left the house you would just have to make sure 3G was on (so you would have to get it from Sprint). Also the mic on it is pretty bad from what reviewers are saying, so you would need a bluetooth headset.
Edit: Forgot to point out Google voice won't make calls over 3G, hence why you would need Skype.
Edit 2: And of course the battery is very good so it makes this setup very possible.