I am ruining into a issue with our exchange 2010 SP2 setup. Everytime I fail over a mailbox DB (DAG) to our colo email on iPhones stop working. I'm thinking that the silent redirection is not working for iPhones it works with OWA no problem. Users are instructed to use mail.xyz.com as the mail server it seems like the initial redirect works because if a user is in the LA site it will automatically change the server on the iPhone to mail-la.xyz.com. I have attached a quick dig to help.