Here are some criteria that you should look at when buying a phone card:

Possible hidden charges
Make sure that you understand the following hidden charges, and always check whether they apply to your calling card:   

-Connection Fees: As long as your call is connected you will be charged, regardless of whether your call is picked up. So, repeated phone calls to the same telephone number, even if they aren’t picked up, will cost you the connection fee. Theoretically, cards with connection fees are cheaper if you tend to make lengthy calls. Unfortunately, some companies may intentionally disconnect the line so that they can charge you the connection fee again.

-Surcharges: A surcharge is an additional charge on top of the usual charge for a service, imposed for a specified reason.

-Service Fees: Some phone card companies charge a fixed weekly or monthly service fee on top of the per-minute rate.

-Incremental Rates: Say you have two cards, A and B, both with rate of 10 cents per minute. Card A charges you each minute, and card B charges you every three minutes. When you make a 1 minute phone call, card A charges $0.10, but card B charges $0.30! This is perfectly legal, so watch out for it.

Period restrictions
Your card may expire at some set time after being activated, or after being used for the first time, usually three to six months, regardless of your balance. Don’t buy too many cards like this from the same vendor at the same time.

Sound Quality
Since many cheap phone cards use IP (Internet) transmission, the sound quality can deteriorate dramatically when many people use the service simultaneously. If you find the sound quality unbearable, consider paying a little more for a phone card that uses a better network.

Stability of the phone card company
The competitive nature of the phone card business has forced many vendors to shut down their operations. We have heard many stories about unfortunate students who spent a lot of money on phone cards, and then ended up unable to use them. Before you choose a phone card, make sure that the company looks like it will be there in the long run. Of course, it’s difficult to predict which companies will survive, but you can try to look for companies that have been around for a while, have a reliable funding source (check their web site), and are popular with other users.

Online recharge and account management
Many online calling cards now allow you (or even your parents back home) to recharge your calling card’s balance and view your calling history. One good thing about these services is that you won’t be cut off in the middle of a conversation if you regularly recharge your account. Another plus is that you can look at your calling record almost immediately after a call is made.