Roaming for Pre-Paid customers is a more recent development and involves additional investment by operators. This is because Roaming signaling and billing systems are more complex for Pre-Paid services than they are for post-paid services.
For Pre-Paid Roaming, in addition to the initial authentication step, the call-related data must be exchanged in real-time between the visited network and the home network by using a special platform (called CAMEL – Customized Applications for Mobile networks Enhanced Logic), to prevent the balance of the roaming customer’s account from becoming overdrawn.
For Post-Paid Roaming, when the user first switches their phone on, the visited network checks in real-time whether the home network authenticates the customer and authorizes its use abroad. But the data records (CDRs) with the details on each SMS and data session are sent to the home operator with some delay (up to several days).