The Blackberry handles this with their own proprietary, parallel push infrastructure called BEZ (sp?) servers. This is a separate data network that RIM maintains, which has allowed them to be dependent only on the basic radio and IP connectivity that carriers provide.

Bottom-line: RIM takes care of managing the higher-level application logic (i.e. event triggers) and application data, and use wireless carriers as dumb bit pipes. It's an extremely capital intensive, but so far successful model and has remained one of their competitive edges in the wireless market.