How to get warning messages before some activitys mentioned below.

Hi Experts,

i have a requirement to write logic in VA02 or VA03 service for object icon each activity one warning message should call before the activity happen.

Anyone can help me for this requirement.Pls follow the below link for activity's.

http://scn.sap.com/dActivating Generic Object Services Toolbar in SAP Objectsocs/DOC-33485

Any one can help me for this requirement to where i have to implement my logic any user exit is there for this requirement.

Thanks.