By entering * (star) before the extension, you can transfer the caller directly to your co-worker's voicemail without first ringing their phone.
1) Inform the caller that you will transfer their call
2) Press the 'Transfer' softkey (this will automatically place the caller on hold).
3) When you hear dialtone, press * (star), then dial the extension of the co-worker, for example *4455
4) Press 'Transfer' again or simply hang up the phone.
The caller will hear the co-worker's greeting and they will be able leave a message.