get one of the mobile hotspots like the one in this video and use wifi. then you have all you need, good data and calls and you can use whatever sim for data== > cheapest prepaid you can find. No need to hassle with phone soft / hardware .
https://m.youtube.com/watch?v=HFsJxOVir2g

other link for mobile hot spots
http://www.bestproducts.com/tech/gad...wifi-hotspots/