Hi mt_x,

Based on my understanding, services are meant to be used on cross-module communications.
I think you could find helpful the following MSDN Prism chapter at SharedServices section:

• 9: Communicating Between Loosely Couple Components
  

Furthermore, you can see the StockTrader Reference Implementation documentation for Common assembly configuration details:

• StockTraderRI
  

I hope you find this useful,

Gabriel Ostrowsky
https//blogs.southworks.net/gostrowsky