Do you want free cell phone service, or $20 for unlimited everything? FreedomPop offers several plans (if available in your area):
Free - 200 minutes, 500 texts, 500 MB data
$7.99 - 500 minutes, unlimited texts, 500 MB data
$10.99 - Unlimited minutes, unlimited texts, 500 MB data
$20 - Unlimited voice, unlimited texts, unlimited data
You can either bring your own device or purchase one of their products, which vary from 4G LTE smartphones to tablets, and hotspots.
I have the $20 plan and would recommend the same for those who can subscribe.