I buy a 60 minute airtime card every 90 days. At the end of 90 days, I still have 60 minutes left, because I don't use my cell phone at all!
I give my minutes to my wife, who doesn't use all her minutes either. We have hundreds of minutes of air time in the bank!
We each have Nokia Cellular Telephones (cell phones) and we use TrakPhone prepaid service, with a 60-minute airtime card costing $19.97 for 90 days of service ($6.88 per month), including unlimited Long Distance, and no monthly bill!