accessing AFP via VPN from iPhone 3G

Here's what I'd like to do, can anyone let me know if it's possible? I want to connect to my company's XServer (Tiger), via VPN from the iPhone. This is easy. The next part isn't. I want to browse the shares via Safari. I'v tried https://, I've tried afp:// I've even tried smb://. Regardless of what I enter, my error message is "Safari can't open the page because the address is invalid.". I'm using the xServer's LAN IP, although I've also tried the WAN IP, it doesn't work either. It seems like a no brainer to me that an iPhone could connect to an Apple server and at least be able to read some of the pdfs or Word files store on it.