Before switching from a prepaid carrier to an MVNO, make sure you read the MVNO's plan closely.
Some don't allow roaming at all, or only allow a minimal amount (like say, 25 megs of data). Some don't allow tethering/hotspot use, or charge an extra fee for it. Some shut off data when you hit the cap instead of throttling.
You can save money with an MVNO, but make sure you're actually getting the services you need.