On the 3200, Go to VPN and Remote Access >>Remote Dial-In User.
1.) Create new PPTP account as shown below.
On the iPhone, go to Settings >> General >> Network and select VPN, Click Add VPN Configuration and type in the details as shown below.
2.) Create a PPTP account on the iPhone.
Server – Public IP of the remote VPN server (router)
Account – Same as the username created on the 3200 Remote Dial-In User.
Password – Same as the password created on the 3200 Remote Dial-In User.
Encryption Level – The encryption level should be set to Auto.