Founds this on the United site:
If you purchase an Internet plan on board, you can surf the Internet and send emails. Please note that we do not allow the use of our onboard Internet service for voice communication or videoconferencing through a cell phone, Voice over Internet Protocol (VoIP) or any similar device or service. Voice and video calls are expressly prohibited.
http://www.united.com/web/en-us/cont...i/default.aspx
Cut and dry there for UA policy to me. Don't know about the feds.