Possible to change a GoPhone plan without changing the current phone number?

You can always keep your number.  You just want to change your plan at the end of your current cycle (do not change mid cycle). And make sure you provide the right refill amount.  

What happens, specifically, if you change mid cycle? Will our phones and plans not work or immediately change over? Will the new billing due date be changed to the mid-cycle date when we change over? Are the changes significant for plans that are really similar (like the $50 and $45 plans)? I am considering a change today, mid-cycle, and would like to know more about any complications--specifically, if I will lose service and for how long, and anything else that may significantly impact my service. Many thanks!

When you change your plan, the old plan terminates and if there is enough money on the account to pay for your the new plan, the new plan starts then. If there is not enough money to pay for the new plan, service will cut off until there is enough to pay for the new plan.

Ahhh. Ok. Many thanks, for your prompt response. Much appreciated!