Femtocells are "small cellular base stations, typically designed for use in a home or small business. It connects to the service provider’s network via broadband (such as DSL or cable); current designs typically support 2 to 4 active mobile phones in a residential setting, and 8 to 16 active mobile phones in enterprise settings. A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable."
Though esoteric at first glance, most people will get the gist of this cell phone intercept hack.
Summary:
• Can be used worldwide via VPN tunneling.
• Allows eavesdropping, calling, text messaging... via someone else's SIM card.
• Inexpensive.
"In addition to attacks against deployed femtocell access points, it is important to remember how the equipment itself could potentially be used for illegal purposes. It is important that femtocell equipment is only supplied to reputable buyers as failure to do so opens up the possibility of femtocell access points being used to support illegal call selling and traffic routing activities, avoidance of lawful interception, use as a false base station to launch man in-the-middle attacks, etc. Of particular concern is the potential for femtocell access points to facilitate the placement of fraudulent calls on 3G networks." (more)
