Before Exchange 2007 comes and dazzles everyone, you can learn hwo to implement mobile messaging with tools available today – Exchange 2003 SP2 and Window Mobile 5.0 with the the Messaging and Security Feature Pack (MSFP). Read this interesting techincal case study here:
http://www.microsoft.com/technet/itsolutions/msit/operations/mobmess_tcs.mspx