I put my Mint card in the other day and it won't work in my house, only when I get out on the highway, and hit&miss in the driveway. As a comparison, my contract S4 Verizon barely gets a signal but I can almost always make a call, almost always SMS, but it has difficulty with MMS- sometimes they go right away, sometimes they take a long time, sometimes fail. So I know I'm in the fringe. I need to actually check signal levels, will do soon.
I also just got my US Mobile sim card but haven't put it in yet or bought an actual plan, they're a Verizon MVNO; I don't know how much, if any, degraded service I'll experience between V contract & V MVNO. Would appreciate comments from those with experience in this regard.