Here’s a very interesting hack originally developed on XDA-Developers.com which will let you share a 3G internet connection with any WiFi enabled device including an iPhone.
1) Purchase HSDPA or other 3G enabled Windows Mobile Professional device with WiFi.
2) Open Settings->Internet Sharing. Enable IS for Bluetooth PAN.
3) Change HKLMCommConnectionSharingPrivateInterface to “TIACXWLN1” (it should currently be “BTPAN1”).
4) Open Settings-> Connections -> Wi-Fi. Select Network Adapters tab. Click IEEE 802.11b/g Compatible Wi-Fi.
5) Enter IP address 192.168.1.1 and subnet mask 255.255.255.0. Click OK.
6) Select Wireless tab. Add New.. to add the Network name for your ad-hoc network
7) Set the iPhone (or any client computer) to use the same ad-hoc network. Client will receive an IP address from the device.
Also see this post for instructions for doing this with different Windows Mobile devices.
Originally published on Pocketnow on September 28, 2007. More Thought articles from the Pocketnow archive.