Service Management - Service order type and Service Package

Service Management -   Service Call type and Service Package   - Can any one tell me if there is a relationship between the service contract package and the service order type on a Service Order

I have a requirement to make certain service order types billable   -  and these service types are not defined as being included in the service package on the service contract.   However the system only appear to use the service type on the contract and does not check if the type is valid for the service package on the contract. 

There for when the entitlement check is carried out in Service order entry it keeps overriding the Service type and verfiying the order as non billable.