In this chapter, a multi-layer ATM architecture is proposed for the interconnection of current and future mobile communications nodes. Consisting of different ATM node types with respect to switching capability, the proposed architecture is adapted to current 2G and evolving 3G systems as well as future 4G wireless systems, as a common and shared backbone transmission network interconnecting core and access nodes between each other and Internet or PLMN/PSTN. Moreover, facing the huge expansion of transmission interconnection network that will support current and future generation mobile communications, a modification of the standard ATM cell structure is introduced in order to efficiently support user mobility functional procedures. The proposed ATM architecture is integrated over a suitable, with respect to region and capacity, physical interface, consisting of SDH or SONET for wide area topologies, wireless links for outdoor areas and LED-POF combination for indoor areas. Being an interesting alternative over copper or traditional fiber, POF characteristics and performance issues are analyzed.