Mobile Voice System: Transfer calls from your device to another number.
For BlackBerry Device Software version 4.5 or earlier
Transfer a call from your device to another phone number
Depending on the options that your administrator has set for you, you might not be able to perform this task. For more information, contact your administrator.
1. During a call, press the Menu key.
2. Click Transfer.
3. Perform one of the following actions:
o If the contact is in your contact list, click the contact.
o If the contact is not in your contact list, type a phone number. Press the Send key.
4. When you are ready to transfer the call, press the Menu key.
5. Click Complete Transfer.
To cancel the transfer, press the Menu key. Click Cancel Transfer.

Mobile Voice System (MVS):
The chance to transfer calls on BB works like a normal desk phone. With the MVS apps you can also move calls from your desk phone to you Blackberry.
Note: Designed for mid- and large-sized companies, BlackBerry MVS is middleware that serves as a gateway between the BlackBerry® Enterprise Server and your company’s enterprise phone system (Private Branch Exchange or PBX).

Sorry Didnt work for me.