I brought my own Samsung Galaxy, and have a mobile hotspot device on Freedom POP for some time. IMO, call quality is dependent on whether you are connected to Sprint 3G, fair to poor, or their 4G LTE which provides good voice quality overall.
Their best feature is that they provide at least 500mb of free 3G/4G LTE mobile data each month. You can buy more data as needed. Your minutes don't count against your mobile data usage. And yes, they do allow using your smartphone as a hotspot for an additional monthly fee.
I've also had issues with Google Voice not working with Freedom Pop. Overall, I would not recommend Freedom Pop as a primary mobile phone service, other than for the free monthly mobile data.
