This may not prevent you from setting up an AT&T (or other vendor) normal long distance account. Your cellphone vendor may even have something available that could be used with landlines. It would be worth checking out. Of course, if there's a monthly service charge just to keep an (unused) account open, then that would eat up any cost savings pretty rapidly. A higher cost per minute plan might be better than a lower minute cost + service fee plan, if such an option exists. A few phone calls to check out various vendor's offerings couldn't hurt. Sign up for their long distance plan. You don't have to tell them you never really plan to use it (or are incapable of using it given your cable phone service).

Or, if this calling card is just for emergencies, buy yourself a low dollar one from a major vendor and just eat the higher costs and be done with it. Just remember that if you're in some disaster or other situation where you need landline long distance, you'll probably need more of it than you originally estimated.