Not PPTP related: If you can use OpenVPN, it's support on Ubuntu is excellent. Just edit /etc/default/openvpn to default some OpenVPN tunnels to auto-start on boot. On the client configuration, use some passphrase-less certificate and keys, so OpenVPN does not stop asking for a passphrase.
Alternatively, on the PPTP side of things, investigate using /etc/network/interfaces, to define
iface callhome inet ppp
This creates a "callhome" pseudo interface, that is auto-brought-up on boot, that in turn calls ppp's /etc/ppp/peers/callhomeprovider config-file. This does not require any graphical clients. For configuring that, check out the standard PPTP-client's docs.