If you already have your JanusVM working with your iPhone, you can quickly setup your Ubuntu Laptop to use the VPN also. Give a quick sudo apt-get install network-manager-pptp and viola network manager now supports pptp configuration. Give a reboot, and you can configure the settings.
I was having a little trouble with the configuration at first, because I was accustomed to the automatic configuration of the iPhone. In the settings you want to enable peer authentication, and refuse chap. Also I had to disable compression otherwise authentication was failing. Then enable all three encryption options. Save, exit, attempt to connect. Enter the username and password you configured in JanusVM and you should connect just fine 
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iPhone Configuration
Step 1: Click the settings button
Step 2: Click the general options menu
Step 3: Click the network menu
Step 4: Click the VPN menu
Step 5: Click the settings menu
JanusVM works with PPTP, therefore use this tab. In the server section add the external ip address of your home machine. If you have a domain name pointing to your external ip address you can also enter that here. If you have a router you will have to use “port forwarding” to forward port 1723 to the ip address of the local machine running JanusVM. In JanusVM option 4 allows you to create users, and passwords. Configure JanusVM according to your liking.
Back to the iPhone.
Step 6: In the account section add the username that you configure in option 4 of JanusVM
Step 7: For “RSA SecurID” turn it off.
Step 8: In the password section add the password you set in option 4 of JanusVM
Step 9: JanusVM requires your iPhone encryption level to be set to “maximum”
Step 10: Set your iPhone to “send all traffic” through the VPN
Remeber, to configure JanusVM you will actually have to boot the virtual machine first. The list of option are automatically displayed once fully booted. I recommend using a static local ip address; if you choose dynamic you will most likely get a different ip address each time you boot JanusVM. This will be a pain, because you will have to adjust the “port forwarding” option in your router as per the local ip address of your JanusVM instance. If anyone has any questions just post a commend. I’ll help get you running ASAP.
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I highly recommend JanusVM for your iPhone VPN solution. Janus incorporates squid, tor, and privoxy providing much more than just a VPN. Squid is a proxy server, which will speed up your connection slightly. Tor is a network of servers around the world that will scramble your network traffic so its practically impossible to track who or where you are. And privoxy will strip all sensitive data from your website browsing to further improve your wireless security. Obviously the VPN part of Janus will allow your iPhone to have a secure connection to the internet, so you can access wifi anywhere without fear of anything!!!
The best part is JanusVM is that it’s completely free. I highly recommend donating a little money if you have it. The author of the software is providing a great service to the open source community, and now allows iPhone users to have a secure, reliable, and instant VPN solution!
http://janusvm.peertech.org/
Just pop JanusVM into a VirtualBox machine, and setup host networking to grab an external ip address. Configure your iphone to access your external ip address, the associated pptp port (port 1723), and viola your VPN should be up and running in about 15 minutes worth of configuration
In the future I will post a graphical tutorial on this, but for now try searching this blog, in the upper right hand corner, for more information about setting up virtual machines and configuring host networking.
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