We've had our Verizon air card account ever since they came out with it...
Have been to AR, TX, MS, FL, GA,NC, SC, VA, MD, PA, & NY and have had internet in all place....even places where the cell phone signal has been really Iffy, like here at our homebase...(no cell phone signal, but we get out on the air card with an external antenna.)....of course, the air card has been updated a couple of times when they update the service....We love it!!!! Now, yes, there are times because of the tower issues, things get a little slow, or they time out, but can live with that.....and when there is wifi the system will give you the option of using it....but we stick to the air card.....on the $60/month plan....and have never been charge over usage....my understanding is that unless you are downloading lots of music or lots of movies, you won't be charged over usage....
Okay, that's our experience....won't leave home without it!!!
BTW.....we also have a router for our air card....and Verizon air card works at the site of the PA GTG.....