btw, i noticed a few things different on the FAQ linked to d_fisher above:
first and foremost is the line about BES users
"If you are at a company and you are on a BES 4.0, your Administrator must enable the "BlackBerry IPModem" setting on the BES. This is a new setting in the Version 4.0 of BES"
i'll have to check on that in the morning....... as i am on BES and i doubt that setting has ever been messed with
also that FAQ says it needs one's T-Mobile username and password, maybe that changed since that was posted and now just allows blank passwords