[stach]

[QUOTE=christerwhitworth;1518253] Today, noticing that Sprint is now marking all those messages as read. QUOTE]

I'm assuming you had already read the messages "Sprint is now marking read" previously on your Berry. It sounds that you want it to behave like a pop3 as opposed to an imap. imap behaves as though you are reading/downloading the email 1st hand (so when you read it on your device -gmail reflects that it was already read).
Below is a copy from the Verizon BIS email set-up (I'm a Verizon cust), I'm pretty sure it will work, -you can go to the Sprint BIS set-up to confirm.
-Good Luck

"About wireless email reconciliation
Depending on your messaging service plan, this feature might not be supported.
Email messages that you open or delete on your BlackBerry® device might be marked automatically as opened or marked automatically as deleted in your integrated email account. Generally, changes that you make to email messages in your integrated email account are not reflected on your device.

If you add an email address to the BlackBerry® Internet Service and delete an email message from your email account inbox, the change is reflected on your device. If you turn off wireless email reconciliation on your device, deleted email messages do not synchronize between your device and your integrated email account.

If you have a Microsoft® Outlook® Web Access work email account, an IMAP email account, or an Windows Live™ Hotmail® email account, email messages that you send from your device are copied to the sent items folder in your email account. Likewise, email messages that you delete are copied to the deleted items folder (except for Windows Live Hotmail).

Note: Depending on your type of integrated email account or email account setup, wireless email reconciliation might not be available for your device.
If you have a work email account that uses Microsoft Outlook Web Access version 5.5, email messages that you send from your device are not copied to the sent items folder in your email account.

Depending on your wireless service provider, wireless email reconciliation for the sent items folder on your device might not be available for your Windows Live Hotmail email account."