How do you locate the serial number for a blackberry 9780?

Depending on your wireless service provider, your BlackBerry® device will have either an IMEI, ESN, or MEID. They are all equivalent.
To retrieve it, perform one of the following actions:

* On your device, in the device options, click Status.
* Search for the PIN and IMEI, ESN, or MEID information on the outside of the box that your device came in.
* Turn off the device and remove the battery. Search for the sticker with the PIN and IMEI, ESN, or MEID information.