memory clarification

[ElAguila]

I have been searching and reading and I am trying to get something clear in my head about the memory management on the mogul. When I install apps, it installed them into the rom space. There is only 64mb of ram. When I start the phone up, I only have 1 app running and that is a small call block software but I only have 15mb of ram free. What is taking up all of the ram? Is it the windows and associated programs/services? If so, is the only way to reduce it to build my own custom rom?