For our winter long travels in the US we do the following:
Phone is Tracphone which is available at Walmart and other places. As long as you have both time and minutes remaining it keeps carrying over. Coverage has been good all over the Southern part of the US.
Data is with Straighttalk. You buy the unit and have a choice - either a monthly plan or buy cards to reload the unit with data capacity. We buy cards and reload as needed. A single reload is good for 2 months. There is no carry over.
This has worked well for us.