The free calling and texting app Textnow which formerly only worked on Wifi or with a paid subscription is now offering Free cellular service through the Sprint network. You just pay once for a $9.99 SIM activation kit and never need to pay a monthly fee or anything again. The Free part is only Voice and text. Their voice and texting does use mobile data but mobile data can't be used for anything else like surfing the Internet unless you pay extra. It does of course have ads to pay for this service but I haven't found them any problem. You have your own phone number and it automatically will switch between available Wifi and cellular for calls and texting. Great idea in my opinion for an extra phone number or backup phone or even a primary phone if you are in a good Sprint network area. Your phone must be compatible with Sprint's network (CDMA) or you can buy refurbished phones from Textnow that are all set to go.