Deleting email doesn't archive messages on Gmail

[hp215]

Hi!

I have my Gmail (it's actually Google Apps account) set up on my BlackBerry 8900 with T-Mobile.

When I read a message on my BB, it does mark it "read" when I log into gmail.com from my computer. However, when I delete a message on BB, both on "Mailbox & Handheld", emails are not archived on Gmail.com side.

I just looked at my friend's blackberry (she has Verizon), and when she deletes it, the email is archived on Gmail.com.

Neither of us are using Gmail IMAP. (we just added the email address and password to set up Gmail without manually adding the IMAP address.) I took a look at her Settings under Gmail, and they are exactly the same as mine--POP is enabled, and "keep mail's copy in inbox". IMAP is enabled. Advanced IMAP settings from Google Labs is NOT enabled.

Is it because she is on Verizon and I'm on T-Mobile? Shouldn't they behave the same regardless of which carrier we use?

Thanks!