No problem! 

If you are on a monthly plan, you can Pause your billing at any time without losing any of your groups, members or messages. When you need to use CallingPost again, simply log in an Un-pause your billing. You will be billed right away when you Un-pause your account and you will be able to send messages right away. 

Otherwise, you can use a Pay As You Go plan  to purchase as you go!

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