I speculated:

Speculation: The "A5 `scrambling code'" is used as the spreading code for a spread spectrum radio.

But I now belive I was wrong. A reader, who I will allow to remain unnamed, informed me that there is only one SS cellular comunication system -- interestingly enough they were using it at the time! They told me that the GSM system is narrow band. So I now ... Speculate: The "A5 `scrambling code'" is an actual cypher system. But the key is negociated between the phone and the cell, not the phone and the other phone. j'