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1) Make sure you have a device password set, see https://wikis-mit-edu.ezproxyberklee.flo.org/confluence/display/bbrelease/Setting+up+device+password+-+BlackBerry+8830
2) Once you notice that you have lost your BlackBerry, on your computer go to the BlackBerry Internet Services (BIS) webpage.
Verizon: https://bis.na.blackberry.com/html?brand=vzw
Sprint: https://bis.na.blackberry.com/html?brand=sprint 
3) Assuming you used the BIS webpage to setup your device's email, login with your BlackBerry Internet Service username/password.
4) Under "Valid Email Accounts" find your MIT account. On the far right of the page, click on the trashcan under "Delete".
5) On the left pane, click on "Service Books", Then click on the "Send Service Books" button.
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You do not need to create a new BlackBerry Internet Services account when you receive your replacement BlackBerry. You will need to tell the BIS service to look for the new device by doing the following steps.
On your Computer:
1) Log into your BlackBerry Internet Services account.
Verizon: https://bis.na.blackberry.com/html?brand=vzw
Sprint: https://bis.na.blackberry.com/html?brand=sprint 
2) In the left pane, click on "Change Device". You will be asked for the devices ESN and PIN numbers.
On your Device:
3)Go to Options -> Status.
4) Within Status you will see the device's PIN and ESN use the "ESN(dec)". Enter the PIN and ESN(dec) number into the fields.
On your computer:
5) Enter in the information exactly as you see it on the device.
6) Click Save.
7) On the left pane, click on "Service Books", Then click on the "Send Service Books" button.
This will now assign the new device to your existing BIS account. Give the service a few minutes to provision the device. To setup your MIT email account, see https://wikis-mit-edu.ezproxyberklee.flo.org/confluence/pages/viewpage.action?pageId=11606055