Rem.Order plan in Assigned values

When I plan a service activity, the cost plan in that activity also is flowing to Assigned values,though No PR has been generated for that service activity,bcoz of this I am not able to release partial budget.As per my understanding the Rem.Order Plan also flows to assigned values.whereas in the in the case of materials,though i plan the material costs,only after generating the PR the values flow to assigned values.Can the same facility be set for Service activity also???