There are 2 primary ways to do this:
1. The easiest is to receive your voicemails via email with transcription and just forward the email. That doesn't make sense in all situations, however.
2. You can dial into the voicemail system by calling 999. Listen to your messages that way, and option 5 after you've listened to the message is "forward to another user". You just enter their extension number and you should be good to go!