You can force the 9630 to use GSM instead of CDMA, but you cannot force it off Sprint. That is disabled by Sprint. It's under Options > Mobile Network.
Like Midnightdraven said, there is no way to stop email from coming at certain times. It's an all-or-nothing thing as the BlackBerry is designed so mail always shows up. With the Treo you could set a schedule, or manually poll your different accounts. BlackBerry has no such scheduling feature. It's always on. You can log into your BIS page and set individual accounts to not forward mail to the handheld, but then to start it again you have to log back in and change the setting manually. Not a convenient solution. Plus, any mail that came in while you had it set not to forward to handheld will not be forwarded when you turn it back on.
Bidaci has the only practical solution for not getting all your messages in the messages folder. You can hide it and leave the individual mail folders as visible. Just be sure to use a separate folder for SMS/MMS messages before you hide the main Messages folder. Open the Messages folder, use Menu to access Options > General Options and go to "SMS and Email inboxes". Set this to "Separate" before hiding the general Messages folder or you won't see your SMS/MMS messages.