I use gmail hosted for my domains email.
When I tried to add it to blackberry directly, it refused.
Here's what I did to make it work with pop access via gmail.

Add another valid email, like a regular gmail account.
Once it's in, go into the 'set up internet email'. (via t-mobile.com for me)
click the Edit icon.
Enter your account info and set it to use pop and SSL.
you might have to do this via the advanced tab.
the screens change depending on configuration. (irritating)

It's a bit wonky, but I got it to work after a few tries.
The account name will stay blah@blah.com, but you'll get your stuff properly.