I was successfully using my Android L2TP VPN Client to connect to my DSR-250. However my phone has now upgraded to Android 4, which does not have an L2TP client. So I configured PPTP on the DSR and PPTP on the android. I have not had any luck in getting this to work, not matter what I try.
I can connect from a PC no problem to the PPTP VPN on the DSR Router.