Forward your cell phone to an airfone
At least Verizon wireless customers can do it inexpensively according to this news release from Verizon. According to the news release, Verizon wireless customers will be able to forward their cell phone to Verizon airfones and will be charged only $0.10 per minute directly to their Verizon bill (useful especially for business travelers whose bills are paid by their company). There is a $10 per month subscription fee to qualify for this low rate; if you don't pay the subscription, the cost is $0.69 per minute, which is still a very good discount off of the regular cost of airfone calls.
Verizon provides airfone service on Continental Airlines, Delta Air Lines, United Airlines, US Airways and Midwest Airlines.