Reply #53: I'm a private pilot.

[Kingshakabobo]

I've used a phone @ 5,000 feet (above sea level)near Chicago.

Also, I've heard of pilots using them on the flight deck at altitude.

Also:

http://www.cmu.edu/PR/releases06/060228_cellphone.html

The researchers found that on average one to four cell phone calls are typically made from every commercial flight in the northeast United States. Some of these calls are made during critical flight stages such as climb-out, or on final approach. This could cause accidents, the investigators report.