I will answer this although it seems to be worded sketchy. Calling cards, and credit cards do not work in a manner as you infer/interpret. In a calling card system, especially pre-paid cards, when you make a call it works like this:
You --> call pre-paid number to enter a PIN
PIN System --> you "What is your PIN #"
You --> enter your PIN
PIN System --> let me check this PIN against my DB and see how much money is available
As described above, the calling card is nothing more than an identifier (PIN) that gets authenticated (Calling card number you call), then a determination is made based on that PIN: "We used that specific PIN as a pre-paid $5.00 calling card... Caller used X amount of minutes. "Enter the number you wish to call" (this is how many minutes you will have to make this call)"
Most calling card platforms have since moved over to either entirely VoIP, or a hybrid combination (VoIP + POTS lines) since it is cost-effective, and generates more revenue. Many of these PIN/calling card systems sit behind an SBC (Session Border Controller) that have controls in place to detect fraudulent activity. Aside from that, let's look at the "security" via way of legalities of what you are asking for...
Assume you could "program" a card and add money. Don't you think, that at some point in time, an organization won't notice the discrepancy based on the amount of calls you made? You would make it easier for authorities to track you since they would have the numbers you called, and the number you are calling from. For anyone not familiar with telephony, do not think blocking caller ID would help you. (That description/wording is for another question (ANI, CNAM, CID, LEC, ILEC, CLEC))