All manner of functions are now outsourced by businesses - from HR, through customer services to IT, and now all sorts of telecoms services. Many retailers are now offering mobile telephony, which is usually supplied and managed by a third party and branded with the retailer's name that the public trusts. There is, however, one type of outsourcing in the telecoms industry that has taken the US by storm, but that seems to have left Europe cold, or at least so far. I am talking about outsourced billing - the outsourcing by a telco of part or all of its revenue management process. Under revenue management, I would include mediation, interconnect, rating, billing, printing bills and delivery to the end customer via the post or the Internet.
Revenue management is by definition mission critical to the Telco.
The fact that outsourcing revenue management is such a serious matter does not explain the differences between the US and European markets. I believe there are several reasons for this. One of the main ones is the size of the operator. Europe, on the other hand, is still in the process of deregulation. The main telcos remain the former PTTs, but as new operators are launched their customer bases change greatly.