Cell phone plans filter: I want a cell phone-sized Android device to mostly use on WiFi, and the Nexus 4 may be the right one. But I might use occasional cell voice & data - help me get that voice & data as cheaply as possible.
(Please ignore tablets for this question, that's an entirely different question. Also, I'm aware that the Nexus 4 does not have LTE so its cell data connection will be a bit slower than my Bionic's)
Short version: I want to buy a Nexus 4 without a contract and mostly use it on WiFi, and I would like to have the option of turning on cell voice and data service 1-2 days per week so just pay $1-$2 per day (so $5-$20 per month instead of $60-$100 per month). How can I do that?
Long version: I already have a Droid Bionic, which is good but has slowed down since it was upgraded to ICS. I work at home and my workflow is centered around using my cell phone as a pager (using Gmail filters), so while at home I only need a WiFi connection. I spend 99% of my time connected to WiFi, so I was thinking it would be nice if I could get a mobile-phone-sized WiFi-only Android device to use at home, but these don't seem to exist. At home I have a VoIP phone and don't use my cell phone for calls, so the cellular connection isn't important - just the data connection through WiFi.
Then I realized the Nexus 4
could be that WiFi-only device. I'm a die-hard Android user and I like the idea of getting a brand-new Nexus device for $300 without a cell phone contract. What I would like to do is buy a Nexus 4 and mostly use it as a WiFi-only device. I would keep using the Bionic as a cell phone and carry it with me when I'm out of the house, but most of the time I'm at home on WiFi and would use the Nexus. (Yes, 2 devices is a complicated setup, but I enjoy geeking out on complicated setups. Juggling 2 devices would be a feature of this setup, not a bug.)
However, I would like to have the option of using the Nexus as a cell phone on occasion - once or twice a week I might use it away from home instead of the Bionic, and I would need a few minutes and some data. On average I use 16.5 minutes per day and 75 MB of cellular data per day. I use Google Voice, so on the days that I'm not using the phone I could stop calls from forwarding to the Nexus and (hopefully) it would not receive any calls or texts.
I'm trying to figure out how to do that easily and as cheaply as possible. It seems that T-Mobile has some good prepaid plans that might fit the bill, but how do I turn off my service (and not get charged) 5-6 days out of the week and only switch on service if I want to use it that day? Is there an easy way to tell T-Mobile "switch me off until further notice," and later tell them "turn on my service today?" Or maybe I would have to pull my SIM card so my Nexus doesn't connect and stop Google Voice from forwarding calls so there's no incoming calls? Or are there other cellular providers who will let me turn my service on and off day-by-day?
Help me out - is there a way to have a Nexus to use on WiFi, and connect it to cellular voice & data on some days but not others?