Though it is possible to control, regarding which other learned professionals have already mentioned the steps, you could look at positive aspects of allowing them to enjoy the services a bit more to help them continue an ongoing call rather than abruptly terminate. So, in essence you have all controls and you could influence the choices. Here is additional info which is helpful
Yes, Telco's or CSP's and OEM's of BSS/OSS have perfected this art since 2G days, you have plethora of products, features and Billing, Policy Charging and Rating Functionality engines such as Vortex, MiLife Application Servers, OCS, IeCCF from ALU, now part of Nokia plus similar Billing related standards that are already in place in IMS, LTE specs for managing customers with some special plans or options to either encourage or otherwise restrict them from using the services of a network especially when they are Pre-paid and IN network considers he/she should re-charge. It is a noble initiative from likes of EU in their vision statements of Ambient networks where in they felt, across some national boundaries if you suddenly find your prepaid is no longer valid, it would be difficult for you to communicate effectively a quick info, and with that idea in essence, there are best practices to allow you and me to some times cross the bar of paying or more precisely not paying but still utilize the services on the spur of the moment and later settle it when you go for recharge. This practice is also implemented in RFID driven vehicular controls for use of certain road or toll payments that is automated in many parts of the world and should your vehicle does not have sufficient balance at the time of crossing say an unmanned barricade, the vehicle is still allowed and when you top up, you will discover a negative balance with billing report for substatiation. Hope this clarifies a bit!. Keep up the research, all the best.
