Dear, Raja! Any VPLMN has its own routeing scheme. And if there is no CAMEL agreements between HPLMN and VPLMN operators then VPLMN will route such call according to its own routeing scheme. In Camel case CAMEL SCP substitutes the original dialed short code with service centre directory number in international format. After that the call is established to HPLMN Service Centre.
For allowing this service HPLMN and VPLMN should support CAMEL. There are a number CAMEL functional entity must be deployed in HPLMN: CSE (SCP), SSP, IP.. VPLMN operator needs to administrate CAMEL IN Triggering table in VMSC i.e. VMSC should support SSF (service sitching function). You may see more about CAMEL in 3GPP 22.078, 23.078.