I just set up a pptp server on Debian Linux and I can connect to the server from my iPhone when in the same network as the PPTP server. But when I leave my office network, I can't connect to the vpn. On the router, I have forwarded port 1723 for PPTP but still no luck.
Thx
PPTP uses tcp/1723 and GRE (ip protocol 47).
How you permit GRE traffic depends on the router. Keep in mind though that you typically can only have a single PPTP session that will work through a NAT.