New promotions and packages come out all the time. Also, the subtle threat of taking your business elsewhere may turn up specials that aren't advertised, or force the company to match a competitor's offer. This will be a common theme for choosing a phone plan. Some companies offer a low per-minute rate, but charge a monthly fee or minimum charge. These plans may be ideal if you don't make a lot of long distance calls.
Some carriers charge several dollars a month just to use a dial-around plan.
So if you make just one call a month, you may end up paying more than if you used your phone company's long distance service. So even if your call lasts only a minute, you'll still be charged for three. This could be a connection charge, a usage charge, whatever name the company wants to give it, find out if you're going to have pay more than just the per-minute rate. You just paid almost a dollar for it. They can offer great rates, especially on international calls, but not all cards are alike.