Platform

I only map non-infrastructure towers directly to services.  The rest of the towers are allocated through Applications or a Cost center & Account combination mapping. 

We map such costs (not necessarily from Towers) to Applications (in pre-ATUM 4.0 terms). Then we can map those to individual services, in essence doing what @Kristine Klein described before, or spread it across multiple services. We do this for monitoring- and security-related expenses. We do something similar to network costs too (via Servers).