Initiate Webservices in a SBM transition?

What's the easiest way in SBM to initiate a webservice in a transition? Is there a script needed or can we initiate this a different way? We would like to use a webservice to generate a Word document from a standard template and the information in the SBM database and attach it to the SBM item for external use.

Look forward to anyone's comments or suggestions,