This post provides relevant background http://blog.cryptographyengineering.com/2013/05/a-few-thoughts-on-cellular-encryption.html http://blog.cryptographyengine

This post provides relevant background http://blog.cryptographyengineering.com/2013/05/a-few-thoughts-on-cellular-encryption.html http://blog.cryptographyengineering.com/2013/05/a-few-though... "GSM phones support an 'export weakened' variant called A5/2, which is so weak you can break it in real time."