We always use the cell phone for ALL long distance calls. In fact we have discontinued all long distance service on our home phone, so if we try to dial out long distance, we get a recording instead. (800 numbers still work OK though).
If it wern't for the modem connection to the internet, I'd get rid of the home phone completely. We travel a lot, weeks and months at a time. I hate paying for that home phone line while we're not there. That's one reason I like DirectTV over cable. When we're gone we just call and they shut off service, then turn it back on when we return. Wish the phone company would do that.
As for calling cards, when you purchase them, be sure to check for any expiration dates they have. If you purchase a 100 minute card that expires in a year, and then only use 50 minutes of it during that year, then remember you've actually paid double the minute rate considering what you actually used.