I joined VM about 2.5 years ago.   I had Verizon for many years, but for me to upgrade to a smart phone was going to cost another $60/month over my current $80 /mth for 2 lines.  So I ordered a cheap PayLo phone from VM, activated it and used it for 2 weeks.  Mostly for checking the connection.   After 2 weeks it was almost as good as my Verizon phone.  So I canceled the PayLo phone and returned it (Got my money back). I ordered a Optimus V and activated it.  I never looked back to Verizon again.  For $25 a month I got everything I needed.  Now Verizon has better roaming (When in the Boonies), but I only do that a few times a year and in realitiy, I don't really want to talk to anybody when I'm out having fun.  
Now as far as coverage maps, the VM ones suck.  After a year and 1/2, I upgraded my V to a GSIII.   There is 4g-LTE all over the place even though VM shows none in my neighborhood.   Yes Now I pay $35/mth ($20 for the handset over 2 years), but its alot cheaper than $100 a month the Verizon wanted.