Just to provide full details, I just started over from scratch and followed your steps exactly. When I switch the vpn slider to on, the status bar appears underneath the slider, shows connecting, starting, authenticating, disconnecting, not connected, then disappears. Sometimes it won't show authenticating and go from starting right to disconnecting. Sometimes a window pops up saying 'You were disconnected my the communication device. Try reconnecting. If the problem continues, verify your settings' - it usually says that after getting stuck on the starting or authenticating process for 10 or 15 seconds. I have verified the settings and all is as you and other tutorials say. I've tried to connect to my VPN with wifi on and on 3G and got the same results.
That's where I am so far. Gonna try rebooting the router to see if that has anything to do with the port forwarding taking effect even though several places don't list that as a step (as well as the manual not saying that needs to be done). I doubt it will work afterwards but I need to try. Then I guess its DD-WRT time unless anyone has suggestions. Maybe I can mess with firewall settings even though, again, that wasn't mentioned anywhere I could find info on this.
UPDATE: After the rebooting the router, now when I slide the VPN slider to on on my iPhone, it says connecting, stays there for about 10-15 seocnds, then a windows pops up and says 'The PPTP-VPN server did not respond. Try reconnecting. If the problem continues, verify your settings and contact your administrator' Well I've verified my settings and then contacted myself and told myself I have no idea what the hell is wrong with this.