I do believe this deserves to be it's own thread. After thinking a bit, with the FreedomPop changes and whatnot, I think its time to sticky good PAYG rates we find as these can be cheap as well. Sure there maybe times where buying it all at once for the year is easier, but at least for me, there are months that I don't use data at all. Hope this helps others as well that may use more on the minimal side like me.
Not exactly what sovashadow probably meant by PayGo, but... An unactivated Tracfone, with a card on hand, makes a good emergency backup phone. $16 will get you a SIM Kit and 500 minutes/500 text/500MB, your choice of carrier. Stick it in a drawer and wait til you need to activate it.
While handy as a backup plan, it's not so smart as a glovebox phone.
There is some question whether refill cards ever expire, but I've used refill cards that were a couple of years old.
In most instances, activation without porting in a number is nearly instantaneous.
Sure: A lot of us (including me), maintain full-time 'backup' phones for 'what if' situations:
What if the MVNO of my primary phone suddenly stops service?
What if I leave my phone at grandma's house (100 miles away).
What if I'm in a different location for work or vacation, and my primary phone doesn't have coverage?
I left my phone at home, and I'm across town in the car. (glovebox phone)
In all of those situations other than 'glovebox', a 'ready to activate' phone that doesn't have active service is almost as useful as one that just needs to be turned on, and with no monthly carrying cost.
You could do something similar with an inactive Tello-ready or Red Pocket-ready setup, but the Tracfone option offers easy access to 3 carriers, and I believe it can be activated without outside internet access.