So essentially, we cannot save a customer's credit card info under the customer profile unless we obtain it via phone or in-person? Even if we receive the customer's credit card through an invoice the very first time, are we also unable to save the card under the customer profile so that we can charge them in the future without an invoice? 

The reason I am asking is because my customer's expenses could vary from month to month - and I'd like to avoid late payments or high A/R receivables. I would rather have the customer's CC information on file so that I can record a sales receipt each month and send the customer a receipt (instead of an invoice). Does that make sense?