Hi Jesus -
Great question. ArcFM Solution 10.2.1b (and all of the ArcFM Solution 10.2.1x releases) is supported only with ArcGIS for Desktop 10.2.1 along with any of Esri's utility or communications specific patches. ArcGIS for Desktop 10.2.1 is the best place to be for performance and stability and both Schneider Electric and Esri have committed to making 10.2.1 the best release for utilities. For more information see the link below.
FAQ: Our Support for Esri's Utility and Telecom... |exchange
Now, it is worth mentioning that this policy only applies to ArcGIS for Desktop. ArcGIS for Server can be upgraded to releases beyond 10.2.1. Be sure to check the supported versions page to ensure that your version of ArcFM is compatible with the version of ArcGIS for Server that you're targeting for an upgrade.
Space: GIS Support |exchange
I hope that helps.
