Best answer by BobTheElectrician
No data on either side is required for regular texting. And a few emergency phone calls will not actually break the bank either.
The $5 will be charged again at the end of the sender's billing cycle, if needed. Suppose your billing date is the 4th of next month, sending the first text on the 3rd and then one other on the 5th will result in 2 x $5 with 99 texts left over for free.
So you will have to evaluate when to do the first text or sign on to a longer add-on, which does not depend on billing cyles at all.