To answer the question - yes, you probably can - however Great Call are one of the few carriers that provide emergency and medical support as part of their service. If this is important to you then be really careful before you switch.
Great Call is a carrier that runs off the Verizon network.
As you already know, they offer very affordable plans. However, you are paying $15 a month for 50 minutes which is less than an hour of phone calls for a month - there are some other great value carriers and plans available:
If you own your current phone and its unlocked, then you can also move to any carrier that runs on the Verizon network: