Is there a way to forward iPhone voicemail without setting up a Google voice or Fusion account? Is there an app that forwards voicemail already on the phone?

Thanks,
Sixto
87 300D

Where are you trying to forward it to? If you have AT&T, you can use GSM codes to forward all unanswered or busy calls to any number:

GSM Feature Codes

As far as voicemails already on the phone, but not in the carrier's VM system anymore, you can either jailbreak the phone and download the sound files via FTP directly, or back up the phone to iTunes and extract them from the backup files:

How to Download Voicemail from an iPhone

Not really an app as much as a method to save the volcemails to another device or computer for later listening.

I receive a voice message and I want to forward the message to someone else. It's option 6 at the end of message playback in many voicemail systems. There is no such option in an iPhone.

Sixto
87 300D

Dial into your voicemail from an outside line, Press # during your greeting and enter your password---follow the prompts

Or just hold down "1" on the iPhone till it gets you into the normal, rather than visual, VM system.