The need to allow customers to roam on other provider's networks has long been a challenge for mobile operators, and the requirements of mobile location services only make it more difficult. It is important to understand how roaming for voice services works, because roaming for mobile location services will be similar but more complex.

To allow roaming for voice services in a postpay system, a mobile operator needs to have network elements of its roaming partners updated in the regions in which the subscriber wishes to travel. The network elements detail the subscriber's mobile number and authorization for roaming services and provide the means for authenticating the subscriber. When a subscriber makes or takes a call while roaming, the call detail record (CDR) is rated and the revenue due the roaming partner is calculated and billed to the home mobile operator. The CDRs are also sent to the home mobile operator so they can reconcile. In many cases, a billing clearinghouse is also involved, which collects the roaming CDRs for the mobile operators and provides the reconciliation for billing and settlement purposes.

Providing roaming for voice services in a prepay system is significantly more complicated. Unlike in North America, prepay systems are very common in Europe and could account in part for the very high rates of mobile service penetration. Prepay systems must provide the same authentication, authorization, and reconciliation service as a postpay roaming system, but must in addition make sure a subscriber has not run out of money. It is virtually impossible to provide roaming services in a handset-based prepay system. Fortunately, most prepay systems are now network based, and are able to share information from their intelligent network (IN) node to provide account balance details and call control (start/stop).

Addressing the roaming issue in wireless data is important, especially given consumers' expectations of seamless cross-border coverage (e.g., the United States and Canada in North America and pan-European in western Europe). Location services further complicate the roaming issue, particularly if mobile operators implement different location positioning methods. Handset-based positioning is a particular problem for roaming. Unfortunately, many mobile operators are choosing positioning systems like A-GPS and E-OTD that require network/handset cooperation for best results. The challenge in billing for mobile location services while roaming provides another case for the value of open standards.